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Professor Mark Hoffman

Deputy Vice-Chancellor (Academic) and Vice-President

Office of the Deputy Vice-Chancellor (Academic)

Deputy Vice-Chancellor (Academic) and Vice-President

Professor Mark Hoffman is the Deputy Vice-Chancellor (Academic) and a Vice-President of the University of Newcastle.

In this role he is responsible for the academic activities of the University including its education programs, encompassing: enabling and pathways programs; the Wollotuka Institute for advancement and leadership of Indigenous education; and education innovation and technology. His portfolio includes student health and wellbeing, work integrated learning, careers and employment, academic administration and student conduct. Prof Hoffman’s responsibilities include academic promotions and staff and student equity, diversity and inclusion.

Mark Hoffman

About Professor Mark Hoffman

Professor Mark Hoffman is an experienced senior leader in the higher education sector who values a collaborative and global focus. He believes that universities are a catalyst for social and economic advancement, of both individuals and society; universities’ primary purpose is to educate and graduate students equipped to lead that advancement, regardless of background, through a seamless interface with industry and society.

As Deputy Vice-Chancellor (Academic) and Vice-President of the University of Newcastle, Mark Hoffman is leading a transformation of the academic programs of the University focussed on ensuring the University’s highly-regarded graduates are Life-Ready. The goals of this major stream of the University’s Looking Ahead Strategy are to: build technology which provides high quality and accessible education; ensure all students have a workplace experience and; that they are healthy and well, and graduate robust and prepared for the challenges of an innovative, fast-changing and diverse workplace.

Prior to his appointment at the University of Newcastle, Mark Hoffman was UNSW Sydney Dean of Engineering from 2015-20 where he created and led a high-quality leadership team, educating over 16,000 students, with a staff of over 800 and revenue of nearly A$500m. During his tenure, UNSW Engineering rose to be #1 in Australia across all four Rankings (QS, Times, AWRU and US News) and comfortably in the top 50 globally. He was instrumental in the creation of Design Next, the London-based TEDI and the number of female engineering professors increased three-fold.

From 2012-15, Professor Mark Hoffman was Pro-Vice Chancellor Research at the University of New South Wales. He has held the roles of Associate Dean Research in the Faculty of Science (2009-2012) and Head of School of Materials Science and Engineering (2007-12), holding both roles concurrently for three years. He chaired the University Committee on Research (2010-13).

Professor Hoffman completed his Bachelor of Engineering, as a cadet with the NSW Electricity Commission, and PhD from the University of Sydney and Masters of Business and Technology from UNSW. He has broad international experience having studied at UC Berkeley, University of Tokyo and Tokyo Metropolitan University. He has held positions at Darmstadt University of Technology, Germany, and the Indian Institute of Science.

Professor Mark Hoffman is a leading materials scientist and engineer, specialising in the structural integrity of materials including piezoelectric and structural ceramics, composites and biological materials. He has published over 250 peer-reviewed papers and attained over $11m in competitive research funding and support from industry. Over 30 higher degree research students have completed their studies under his supervision. He is a Fellow of the Australian Academic of Technological Science and Engineering and Engineers Australia.

Professor Hoffman was recently a member of the Excellence Commission for the German Science Foundation and currently chair of the Engineering Panel for the 2020 Hong Kong Research Assessment Exercise. He is a Board Member of the Australian Academy of Technological Sciences and Engineering, and previously of the International Congress on Fracture.

Deputy Vice-Chancellor (Academic) and Vice-President

Professor Mark Hoffman is the Deputy Vice-Chancellor (Academic) and a Vice-President of the University of Newcastle.In this role he is responsible for the academic activities of the University including its education programs, encompassing: enabling and pathways programs; the Wollotuka Institute…

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Career Summary

Qualifications

  • Doctor of Philosophy, University of Sydney
  • Bachelor of Engineering (Mechanical Engineering) (Honours), University of Sydney
  • Master of Business and Technology, University of New South Wales

Professional Experience

UON Appointment

Title Organisation / Department
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Publications

For publications that are currently unpublished or in-press, details are shown in italics.


Chapter (7 outputs)

Year Citation Altmetrics Link
2015 Borrero-Lopez O, Hoffman M, 'Sliding-contact fracture of brittle layers', Thin Films and Coatings: Toughening and Toughness Characterization 529-589 (2015)

© 2016 by Taylor and Francis Group, LLC. Sliding is one of the most common contact configurations for materials used in engineering applications. It occurs wherever contacting par... [more]

© 2016 by Taylor and Francis Group, LLC. Sliding is one of the most common contact configurations for materials used in engineering applications. It occurs wherever contacting parts are in relative motion, for example, in rotors, stators, pistons, and other wear parts of both large- and small-scale engines (i.e., microelectromechanical systems, MEMS). Moreover, sliding contacts may appear when third bodies impact a material at low angle, for example, slurry pump impellers. In sliding contacts, the friction between the contacting bodies creates relatively complex stress fields due to the presence of tangential forces in addition to normal forces. This, in turn, results in a wider range of possible failure modes in materials subjected to sliding compared to uniaxial contact loaded normal to the surface.

DOI 10.1201/b18729
2013 Hoffman M, 'Fracture Resistance of Ceramics', Ceramics Science and Technology 601-631 (2013)
DOI 10.1002/9783527631940.ch26
2010 Hoffman M, 'Fracture Resistance of Ceramics', Ceramics Science and Technology 601-631 (2010)
DOI 10.1002/9783527631735.ch14
2006 Hu X, Hoffman M, Liu HY, 'Preface', Fracture of Materials: Moving Forwards (Key Engineering Materials), Scientific.Net, Germany (2006)
2004 Tilbrook M, Moon R, Rutgers L, Hoffman M, 'Effective thermomechanical properties of interpenetrating-structured composites', Composites Technologies For 2020 94-99 (2004)

Composites exhibiting an interpenetrating structure have received recent attention for their potential improved toughness properties. Numerous models for prediction of effective p... [more]

Composites exhibiting an interpenetrating structure have received recent attention for their potential improved toughness properties. Numerous models for prediction of effective properties of composite materials have been developed, however these have tended to focus on traditional composite structures. Alumina/epoxy and alumina/aluminium composites with interpenetrating structures were produced via a multi-step infiltration process, and their mechanical properties investigated via the impulse excitation technique. Effective properties of these specimens and other interpenetrating-structured composites appear to be predicted most successfully using the effective medium approximation (EMA). The EMA does not specify internal geometry, but rather considers inclusions of each constituent phase situated within an effective medium, which is appropriate for the non-periodic structures ofthe composites investigated.

2004 Tilbrook M, Rutgers L, Moon R, Hoffman M, 'Fatigue crack propagation in graded composites', Composites Technologies For 2020 331-336 (2004)

Material structures exhibiting a tailored variation in properties are collectively termed functionally graded materials (FGMs). Despite the considerable advances in understanding ... [more]

Material structures exhibiting a tailored variation in properties are collectively termed functionally graded materials (FGMs). Despite the considerable advances in understanding of FGMs over the past decade, several key areas require further work, including the fatigue behaviour of, and crack propagation paths in, FGMs. Graded alumina-epoxy composite samples, exhibiting an approximately continuous spatial variation in composition and properties, have been produced via an infiltration process. Fatigue cracks have been initiated and propagated under cyclic four-point bend loading. Crack deflection has been observed, along with subsequent deviation and curvature as the crack moves through the graded region. A variation in fatigue crack growth resistance was observed as the crack moved through regions of varying composition. A finite element model, which employs automatic crack extension and remeshing, has been developed to simulate the propagation process. Particular attention was paid to the criteria used for crack propagation and deflection, and to the effects of bridging on crack path. Experimental results and modeling predictions are presented and compared.

2003 Furukawa T, Yoshimura S, Hoffman M, 'Implicit material modeling for temperature-dependent viscoplasticity using multi-layer neural networks', , ELSEVIER SCIENCE BV 280-283 (2003)
Citations Scopus - 5Web of Science - 4
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Journal article (208 outputs)

Year Citation Altmetrics Link
2020 Shi X, Kumar N, Hoffman M, 'Electrical fatigue behavior of NBT-BT-xKNN ferroelectrics: effect of ferroelectric phase transformations and oxygen vacancies', JOURNAL OF MATERIALS CHEMISTRY C, 8 3887-3896 (2020)
DOI 10.1039/c9tc05665c
2020 Kumar N, Kong S, Sharma P, Sharma P, Shi X, Vats G, et al., 'Functional surface layers in relaxor ferroelectrics', Journal of Materials Chemistry C, 8 7663-7671 (2020)

© The Royal Society of Chemistry. Relaxor ferroelectrics are technologically important materials for applications in, for example, high-temperature capacitors, transducers and nan... [more]

© The Royal Society of Chemistry. Relaxor ferroelectrics are technologically important materials for applications in, for example, high-temperature capacitors, transducers and nano-positioning systems. These materials have often been reported to exhibit surface or skin layers with distinct physical properties to the bulk. The control of formation and functionality of these skin layers has remained elusive and is becoming increasingly critical due to device miniaturization, where the surface contribution to overall material properties becomes significant. We recently demonstrated that the distinct structural distortion of the skin layer is intimately related to the internal chemical pressure applied by oxygen vacancies and the plane stress conditions at the surface. (S. Kong, N. Kumar, S. Checchia, C. Cazorla and J. Daniels, Adv. Funct. Mater., 2019, 29, 1900344) Here, we demonstrate a unique capability to control the formation and properties of the skin layer through the control of defect concentration. Most interestingly, the skin layer is polar and both electrically and optically active, making it functional and a new candidate for low operating voltage and/or optoelectronic devices. The surface domains in the skin could be altered by applying a small voltage bias (1000 times lower than bulk) or light illumination. A reversible optical change in surface domains provides a new non-contact external control to tune the material polarisation.

DOI 10.1039/d0tc01300e
2020 Arsecularatne JA, Colusso E, Della Gaspera E, Martucci A, Hoffman MJ, 'Nanomechanical and tribological characterization of silk and silk-titanate composite coatings', TRIBOLOGY INTERNATIONAL, 146 (2020)
DOI 10.1016/j.triboint.2020.106195
2020 Lee K-Y, Shi X, Kumar N, Hoffman M, Etter M, Checchia S, et al., 'Electric-Field-Induced Phase Transformation and Frequency-Dependent Behavior of Bismuth Sodium Titanate-Barium Titanate', MATERIALS, 13 (2020)
DOI 10.3390/ma13051054
Citations Scopus - 1Web of Science - 2
2020 Lee K-Y, Shi X, Kumar N, Hoffman M, Etter M, Winter J, et al., 'The complex structural mechanisms behind strain curves in bismuth sodium titanate-barium titanate', APPLIED PHYSICS LETTERS, 116 (2020)
DOI 10.1063/5.0005401
2020 Arsecularatne JA, Hoffman MJ, 'The wear behaviour of remineralised human dental enamel: An in vitro study', WEAR, 444 (2020)
DOI 10.1016/j.wear.2019.203165
2020 Kumar N, Shi X, Hoffman M, 'Spontaneous relaxor to ferroelectric transition in lead-free relaxor piezoceramics and the role of point defects', JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 40 2323-2330 (2020)
DOI 10.1016/j.jeurceramsoc.2020.01.066
Citations Web of Science - 1
2019 Esslinger S, Neumeister P, Schoenecker A, Hoffman M, Studer A, Hinterstein M, 'In Situ Neutron Diffraction Studies on Poling of the Hard PZT Ceramic PIC181', ADVANCED ENGINEERING MATERIALS, 21 (2019)
DOI 10.1002/adem.201900159
2019 Kumar N, Shi X, Jones J, Hoffman M, 'Electrical fatigue failure in (Na1/2Bi1/2)TiO3-BaTiO3 relaxor ceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 102 5997-6007 (2019)
DOI 10.1111/jace.16475
Citations Scopus - 1Web of Science - 1
2019 Wu Y-Q, Arsecularatne JA, Hoffman M, 'Effect of acidity upon attrition-corrosion of human dental enamel (vol 44, pg 23, 2015)', JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, 89 260-260 (2019)
DOI 10.1016/j.jmbbm.2018.08.054
2019 Hinterstein M, Lee K-Y, Esslinger S, Glaum J, Studer AJ, Hoffman M, Hoffmann MJ, 'Determining fundamental properties from diffraction: Electric field induced strain and piezoelectric coefficient', PHYSICAL REVIEW B, 99 (2019)
DOI 10.1103/PhysRevB.99.174107
Citations Scopus - 4Web of Science - 5
2018 Denis LM, Glaum J, Hoffman M, Daniels JE, Hooper RJ, Tutuncu G, et al., 'Effect of mechanical depoling on piezoelectric properties of Na0.5Bi0.5TiO3-xBaTiO(3) in the morphotropic phase boundary region', JOURNAL OF MATERIALS SCIENCE, 53 1672-1679 (2018)
DOI 10.1007/s10853-017-1616-2
Citations Scopus - 5Web of Science - 4
2018 Hinterstein M, Mgbemere HE, Hoelzel M, Rheinheimer W, Adabifiroozjaei E, Koshy P, et al., 'Influence of microstructure on symmetry determination of piezoceramics', JOURNAL OF APPLIED CRYSTALLOGRAPHY, 51 670-678 (2018)
DOI 10.1107/S1600576718003916
Citations Scopus - 5Web of Science - 5
2018 Wu Y-Q, Arsecularatne JA, Warton D, Hoffman M, 'Effect of contact load upon attrition-corrosion of human dental enamel', WEAR, 414 101-108 (2018)
DOI 10.1016/j.wear.2018.08.005
Citations Scopus - 3Web of Science - 2
2018 Kruzic JJ, Arsecularatne JA, Tanaka CB, Hoffman MJ, Cesar PF, 'Recent advances in understanding the fatigue and wear behavior of dental composites and ceramics', JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, 88 504-533 (2018)
DOI 10.1016/j.jmbbm.2018.08.008
Citations Scopus - 25Web of Science - 21
2018 Shi X, Kumar N, Hoffman M, 'Electric field-temperature phase diagrams for (Bi1/2Na1/2)TiO3-BaTiO3-(K1/2Na1/2)NbO3 relaxor ceramics', JOURNAL OF MATERIALS CHEMISTRY C, 6 12224-12233 (2018)
DOI 10.1039/c8tc04189j
Citations Scopus - 7Web of Science - 8
2018 Hoffman M, Zhang L, 'The Rising Importance of Precision Engineering', Engineering, 4 759 (2018)
DOI 10.1016/j.eng.2018.11.007
2017 Nazir MT, Phung BT, Hoffman M, Yu S, Li S, 'Micro-AlN/nano-SiO2 co-filled silicone rubber composites with high thermal stability and excellent dielectric properties', MATERIALS LETTERS, 209 421-424 (2017)
DOI 10.1016/j.matlet.2017.08.077
Citations Scopus - 18Web of Science - 18
2017 WU Y-Q, Arsecularatne JA, Hoffman M, 'Attrition-corrosion of human dental enamel: A review', Biosurface and Biotribology, 3 196-210 (2017)
DOI 10.1016/j.bsbt.2017.12.001
2016 Tang H, Fang M, Min X, Wang X, Huang Z, Wen R, et al., 'Mechanical Properties and Solid Particle Erosion Behavior of LaMgAl11O19-Al2O3 Ceramic at Room and Elevated Temperatures', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 99 2138-2146 (2016)
DOI 10.1111/jace.14205
Citations Scopus - 11Web of Science - 11
2016 Nazir MT, Phung BT, Hoffman M, 'Performance of Silicone Rubber Composites with SiO2 Micro/Nano-filler under AC Corona Discharge', IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION, 23 2804-2815 (2016)
DOI 10.1109/TDEI.2016.7736840
Citations Scopus - 23Web of Science - 20
2016 Glaum J, Zakhozheva M, Acosta M, Aksel E, Kleebe H-J, Hoffman M, Schmitt LA, 'Influence of B-Site Disorder on the Properties of Unpoled Bi1/2Na1/2TiO3-0.06Ba(ZrxTi1-x)O-3 Piezoceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 99 2801-2808 (2016)
DOI 10.1111/jace.14266
Citations Scopus - 7Web of Science - 7
2016 Zhang Y, Glaum J, Ehmke MC, Blendell JE, Bowman KJ, Hoffman MJ, 'High Bipolar Fatigue Resistance of BCTZ Lead-Free Piezoelectric Ceramics', Journal of the American Ceramic Society, 99 174-182 (2016)

© 2015 The American Ceramic Society. (Ba, Ca)(Ti, Zr)O3 ceramics have been considered as a potential lead-free alternative to commonly used lead-based piezoelectric ceramics due t... [more]

© 2015 The American Ceramic Society. (Ba, Ca)(Ti, Zr)O3 ceramics have been considered as a potential lead-free alternative to commonly used lead-based piezoelectric ceramics due to their high piezoelectric performance at room temperature. In this study, the bipolar fatigue behavior of this material is investigated at room temperature. Two compositions were cycled with a bipolar electric field signal at 10 Hz with a maximum of three times the coercive field for up to approximately 107 cycles. Both investigated compositions exhibited high bipolar fatigue resistance compared to other ceramics reported in the literatures. The high fatigue resistance originates from the lack of mechanical damage and a weak domain wall pinning effect due to their location in the phase transition region. It was also found that pore morphology affected bipolar fatigue behavior.

DOI 10.1111/jace.13927
Citations Scopus - 24Web of Science - 22
2016 Zhang Y, Glaum J, Ehmke MC, Bowman KJ, Blendell JE, Hoffman MJ, 'Unipolar Fatigue Behavior of BCTZ Lead-Free Piezoelectric Ceramics', Journal of the American Ceramic Society, 99 1287-1293 (2016)

© 2016 The American Ceramic Society. (Ba,Ca)(Ti,Zr)O3 lead-free piezoelectric ceramics have been considered to be one of the most potential lead-free alternatives for PZT in the r... [more]

© 2016 The American Ceramic Society. (Ba,Ca)(Ti,Zr)O3 lead-free piezoelectric ceramics have been considered to be one of the most potential lead-free alternatives for PZT in the room-temperature range. The stability of the piezoelectric performance during unipolar cycling is investigated in this study. It is found that the unipolar fatigue behavior is similar to soft PZT. Developments of bias field, offset polarization, asymmetry in strain, and dielectric hysteresis loops are observed during bipolar measurements. The changes are mainly contributed to the migration of charge carriers to the grain boundaries driven by the unscreened depolarization field. Redistribution of the accumulated charge carriers by bipolar electric cycling or thermal annealing can significantly recover the unipolar fatigued state. The unipolar strain response stabilized after 1000 cycles at 0.053% for an electric field of 0.6 kV/mm (d33*= 883 pm/V), which is a good characteristic for actuator applications.

DOI 10.1111/jace.14103
Citations Scopus - 12Web of Science - 11
2016 Sims A, Simmons A, Hoffman M, Schindhelm K, 'Facial deformations during nasal continuous positive airway pressure therapy', Journal of Biomechanics, 49 3848-3854 (2016)

© 2016 Elsevier Ltd Obstructive Sleep Apnoea (OSA), characterised by repeated collapse of the pharyngeal airway during sleep, causes cessation of breathing followed by arousal, re... [more]

© 2016 Elsevier Ltd Obstructive Sleep Apnoea (OSA), characterised by repeated collapse of the pharyngeal airway during sleep, causes cessation of breathing followed by arousal, restoring normality. Continuous Positive Airway Pressure (CPAP) is a non-invasive, effective treatment for OSA where positive pressure is applied to the airway through a mask, maintaining patency. Nasal masks are commonly used, contacting the face across the upper lip, sides of the nose and the nasal bridge. Despite health benefits, therapy compliance is sub-optimal, often due to poor mask fit and discomfort. Masks have been designed to conform to the facial profile, but have not taken into account facial deformations. The nature of facial deformations while undergoing CPAP therapy is unknown. This study investigates the facial deformations experienced by a patient while undergoing nasal CPAP therapy. Magnetic Resonance Imaging (MRI) scans of the face were acquired of participants in the reference configuration and while undergoing CPAP therapy. The CPAP scan volume was registered onto the reference volume prior to surface generation for each state. Perpendicular deformation was measured from the reference facial profile to the deformed profile. Large facial deformations were measured at the sides of the nose (4.6±1.6mm) and the upper lip (4.9±1.8mm) with much smaller deformations at the nasal bridge (2.4±0.2mm). When normalised by applied load and tissue thickness, no difference was found. These findings and techniques can be used to consider facial deformation in the development of future nasal CPAP masks to improve comfort and compliance to therapy.

DOI 10.1016/j.jbiomech.2016.10.027
2016 Toth LS, Gu CF, Beausir B, Fundenberger JJ, Hoffman M, 'Geometrically necessary dislocations favor the Taylor uniform deformation mode in ultra-fine-grained polycrystals', ACTA MATERIALIA, 117 35-42 (2016)
DOI 10.1016/j.actamat.2016.06.062
Citations Scopus - 24Web of Science - 22
2016 Hang T, Glaum J, Genenko YA, Phung T, Hoffman M, 'Investigation of partial discharge in piezoelectric ceramics', Acta Materialia, 102 284-291 (2016)

© 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Electrical partial discharges were studied in different piezoelectric ceramics. Epoxy material with mic... [more]

© 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Electrical partial discharges were studied in different piezoelectric ceramics. Epoxy material with micro sized cavities was also tested and compared to the piezoelectric ceramics. It is found that compared to epoxy, partial discharge (PD) occurs at relatively lower electric fields for piezoelectric ceramics. The PD inception voltage was found to be lower for materials with higher relative permittivity. This indicates that the intensification of the electric field within the defects is the main cause for the differences in inception field observed for epoxy compared to piezoelectric ceramics. Furthermore, phase resolved PD pattern analysis was carried out for all materials at elevated electric fields. A broad distribution of the discharge event was observed for both epoxy and hard PZT samples, whereas for soft PZT discharge occurs concentrated at electric fields slightly above the coercive field. This intensification of PDs close to the coercive field suggests that PDs may be enhanced due to an increase of the internal field and electron emission rate induced by the domain switching process.

DOI 10.1016/j.actamat.2015.09.031
Citations Scopus - 6Web of Science - 4
2016 Namsar O, Watcharapasorn A, Hoffman M, Glaum J, Jiansirisomboon S, 'Dielectric properties, electric-field-induced polarization and strain behavior of Lead Zirconate Titanate-Strontium bismuth Niobate ceramics', Journal of Electroceramics, 36 70-75 (2016)

© 2016, Springer Science+Business Media New York. The dielectric properties and electric-field-induced polarization and strain behavior of (1-x)PZT-xSBN (x ranged from 0 to 1.0 we... [more]

© 2016, Springer Science+Business Media New York. The dielectric properties and electric-field-induced polarization and strain behavior of (1-x)PZT-xSBN (x ranged from 0 to 1.0 weight fraction) ceramics prepared by a conventional mixed-oxide method were investigated. The dielectric properties indicated that the dielectric constant of PZT could be enhanced with small addition of SBN (x¿=¿0.1). From the polarization hysteresis loop measurements, it was found that the ferroelectric properties of nominal PZT-SBN ceramics changed strongly from the normal ferroelectric in PZT-rich ceramics to the paraelectric character in SBN-rich compositions. The strain hysteresis loops of nominal PZT-SBN under bipolar electric field loading suggested that the butterfly curve was observed in some compositions (0¿=¿x¿=¿0.3 and pure SBN ceramic). This research clearly showed the significance of SBN in controlling the electrical properties of nominal PZT-SBN ceramics.

DOI 10.1007/s10832-016-0030-5
Citations Scopus - 2Web of Science - 1
2016 Acosta M, Schmitt LA, Cazorla C, Studer A, Zintler A, Glaum J, et al., 'Piezoelectricity and rotostriction through polar and non-polar coupled instabilities in bismuth-based piezoceramics', SCIENTIFIC REPORTS, 6 (2016)
DOI 10.1038/srep28742
Citations Scopus - 17Web of Science - 18
2015 Borrero-Lõpez O, Vodenitcharova T, Quadir MZ, Hoffman M, 'Scratch Fracture of Polycrystalline Silicon Wafers', Journal of the American Ceramic Society, 98 2587-2594 (2015)

© 2015 The American Ceramic Society. Fracture of silicon wafers is responsible for lower than desirable manufacturing yields in the photovoltaic industry. This study investigates ... [more]

© 2015 The American Ceramic Society. Fracture of silicon wafers is responsible for lower than desirable manufacturing yields in the photovoltaic industry. This study investigates the fracture response of polycrystalline silicon wafers under sliding contacts at different length scales, by means of macro and microscratch tests which simulate cutting processes. The dominant fracture modes were found to be partial cone cracking (macro) and radial cracking (micro). Statistical analysis of the critical loads for crack initiation showed that polycrystalline wafers are weaker than their single-crystal counterparts, that is, they crack at lower applied loads under comparable conditions. Moreover, the Weibull modulus of polycrystalline silicon was found to be the average of the relevant single-crystal directions. Subsequent microscopic observations and flexure tests reveal that the lower resistance of polycrystalline silicon to scratch fracture is due mainly to the presence of relatively large polishing defects, and not to the weakness of its grain boundaries. Alternatives are proposed to minimize damage during ingot cutting, with a view to minimizing wafer breakages during wafer handling and machining.

DOI 10.1111/jace.13620
Citations Scopus - 4Web of Science - 3
2015 Hinterstein M, Schmitt LA, Hoelzel M, Jo W, Roedel J, Kleebe H-J, Hoffman M, 'Cyclic electric field response of morphotropic Bi1/2Na1/2TiO3-BaTiO3 piezoceramics', APPLIED PHYSICS LETTERS, 106 (2015)
DOI 10.1063/1.4922145
Citations Scopus - 30Web of Science - 30
2015 Namsar O, Watcharapasorn A, Hoffman M, Glaum J, Jiansirisomboon S, 'Dielectric, Polarization and Strain Response of Enhanced Complex Ceramics: The Study through Pb(Zr0.52Ti0.48)O-3-SrBi2Ta2O9', FERROELECTRICS, 488 79-88 (2015)
DOI 10.1080/00150193.2015.1072037
Citations Scopus - 1Web of Science - 1
2015 Zhang Y, Glaum J, Ehmke MC, Bowman KJ, Blendell JE, Hoffman MJ, 'The ageing and de-ageing behaviour of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O lead-free piezoelectric ceramics', Journal of Applied Physics, 118 (2015)
DOI 10.1063/1.4931892
Citations Scopus - 9
2015 Zhang Y, Arsecularatne JA, Hoffman M, 'The effects of three different food acids on the attrition-corrosion wear of human dental enamel', JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48 (2015)
DOI 10.1088/0022-3727/48/28/285401
Citations Scopus - 7Web of Science - 5
2015 Vodenitcharova T, Kong Y, Shen L, Dayal P, Hoffman M, 'Nano/micro mechanics study of nanoindentation on thin Al/Pd films', JOURNAL OF MATERIALS RESEARCH, 30 699-708 (2015)
DOI 10.1557/jmr.2015.10
Citations Scopus - 4Web of Science - 4
2015 Gu CF, Hoffman M, Toth LS, Zhang YD, 'Grain size dependent texture evolution in severely rolled pure copper', Materials Characterization, 101 180-188 (2015)

© 2015 Elsevier Inc. All rights reserved. Large strain rolling - up to 97% thickness reduction - was carried out on pure copper with two different initial grain sizes: coarse-grai... [more]

© 2015 Elsevier Inc. All rights reserved. Large strain rolling - up to 97% thickness reduction - was carried out on pure copper with two different initial grain sizes: coarse-grained (CG, 24 µm) and ultrafine-grained (UFG, 360 nm). After rolling, classical copper-type rolling texture was obtained for the CG copper while a brass-type rolling texture was observed in the starting UFG copper, obtained by eight-pass equal channel angular pressing at room temperature prior to rolling. Using the Viscoplastic Self Consistent polycrystal model, it is found that the deformation mechanism at large rolling strain is grain size dependent and a change in the major slip mode has a large impact on the type of deformation texture. The brass-type texture in the UFG material can be simulated using {111} < 112¯> partial slip together with {111} < 11¯0 > slip and a small amount of twinning; for the CG material, only {111} < 11¯0 > slip is needed to reproduce the copper-type rolling texture. Further, it is found that the polycrystal deformation condition approaches Taylor behavior in the UFG material whereas much more strain heterogeneity is present in rolling of the CG copper. By orientation imaging electron microscopy the geometrically necessary dislocation (GND) density is found to be decreasing in the UFG rolled samples while increasing in the CG case. This tendency corroborates the texture simulation parameters concerning strain heterogeneity.

DOI 10.1016/j.matchar.2015.02.003
Citations Scopus - 20Web of Science - 19
2015 Hinterstein M, Hoelzel M, Rouquette J, Haines J, Glaum J, Kungl H, Hoffman M, 'Interplay of strain mechanisms in morphotropic piezoceramics', ACTA MATERIALIA, 94 319-327 (2015)
DOI 10.1016/j.actamat.2015.04.017
Citations Scopus - 49Web of Science - 47
2015 Lazo N, Vodenitcharova T, Hoffman M, 'Optimized bio-inspired stiffening design for an engine nacelle', Bioinspiration and Biomimetics, 10 (2015)

© 2015 IOP Publishing Ltd. Structural efficiency is a common engineering goal in which an ideal solution provides a structure with optimized performance at minimized weight, with ... [more]

© 2015 IOP Publishing Ltd. Structural efficiency is a common engineering goal in which an ideal solution provides a structure with optimized performance at minimized weight, with consideration of material mechanical properties, structural geometry, and manufacturability. This study aims to address this goal in developing high performance lightweight, stiff mechanical components by creating an optimized design from a biologically-inspired template. The approach is implemented on the optimization of rib stiffeners along an aircraft engine nacelle. The helical and angled arrangements of cellulose fibres in plants were chosen as the bio-inspired template. Optimization of total displacement and weight was carried out using a genetic algorithm (GA) coupled with finite element analysis. Iterations showed a gradual convergence in normalized fitness. Displacement was given higher emphasis in optimization, thus the GA optimization tended towards individual designs with weights near the mass constraint. Dominant features of the resulting designs were helical ribs with rectangular cross-sections having large height-to-width ratio. Displacement reduction was at 73% as compared to an unreinforced nacelle, and is attributed to the geometric features and layout of the stiffeners, while mass is maintained within the constraint.

DOI 10.1088/1748-3190/10/6/066008
2015 Wu YQ, Arsecularatne JA, Hoffman M, 'Effect of acidity upon attrition-corrosion of human dental enamel', Journal of the Mechanical Behavior of Biomedical Materials, 44 23-34 (2015)

© 2015 Elsevier Ltd. Attrition-corrosion is a synthesized human enamel wear process combined mechanical effects (attrition) with corrosion. With the rising consumption of acidic f... [more]

© 2015 Elsevier Ltd. Attrition-corrosion is a synthesized human enamel wear process combined mechanical effects (attrition) with corrosion. With the rising consumption of acidic food and beverages, attrition-corrosion is becoming increasingly common. Yet, research is limited and the underlying mechanism remains unclear. In this study, in vitro wear loss of human enamel was investigated and the attrition-corrosion process and wear mechanism were elucidated by the analysis of the wear scar and its subsurface using focused ion beam (FIB) sectioning and scanning electron microscopy (SEM). Human enamel flat-surface samples were prepared with enamel cusps as the wear antagonists. Reciprocating wear testing was undertaken under load of 5. N at the speed of 66 cycle/min for 2250 cycles with lubricants including citric acid (at pH 3.2 and 5.5), acetic acid (at pH 3.2 and 5.5) and distilled water. All lubricants were used at 37. °C. Similar human enamel flat-surface samples were also exposed to the same solutions as a control group. The substance loss of enamel during wear can be linked to the corrosion potential of a lubricant used. Using a lubricant with very low corrosion potential (such as distilled water), the wear mechanism was dominated by delamination with high wear loss. Conversely, the wear mechanism changed to shaving of the softened layer with less material loss in an environment with medium corrosion potential such as citric acid at pH 3.2 and 5.5 and acetic acid at pH 5.5. However, a highly corrosive environment (e.g., acetic acid at pH 3.2) caused the greatest loss of substance during wear.

DOI 10.1016/j.jmbbm.2014.12.016
Citations Scopus - 17Web of Science - 17
2015 Arsecularatne JA, Dingeldein JP, Hoffman M, 'An in vitro study of the wear mechanism of a leucite glass dental ceramic', Biosurface and Biotribology, 1 50-61 (2015)
DOI 10.1016/j.bsbt.2015.02.004
2014 Glaum J, Hoffman M, 'Electric fatigue of lead-free piezoelectric materials', Journal of the American Ceramic Society, 97 665-680 (2014)

A considerable body of knowledge now exists from studies involving the development of lead-free piezoelectric ceramics and a number of high potential alternatives to current lead-... [more]

A considerable body of knowledge now exists from studies involving the development of lead-free piezoelectric ceramics and a number of high potential alternatives to current lead-based materials have been identified. Stability under cyclic electric fields is an important property of piezoelectric materials. Here, we review the research to date which shows that fatigue under cyclic electrical loading is prevalent in many lead-free piezoelectric ceramic compositions. However, the variety of compositions and mechanisms for piezoelectric behavior in these materials corresponds to significant variances in the nature of fatigue degradation and the likely mechanisms thereof, which do not directly parallel those of well-studied lead-based materials. In particular, the use of field-induced phase changes as an actuation mechanism provides distinctive fatigue behaviors. Particular attention is given to fatigue of ferroelectric and relaxor (ergodic and nonergodic) structures and their dependence upon temperature and electric field and the potential design of materials with high fatigue resistance. © 2014 The American Ceramic Society.

DOI 10.1111/jace.12811
Citations Scopus - 66Web of Science - 63
2014 Hang T, Glaum J, Phung T, Hoffman M, 'Investigation of partial discharge and fracture strength in piezoelectric ceramics', Journal of the American Ceramic Society, 97 1905-1911 (2014)

Although piezoelectric ceramics are widely used, the structural reliability of these materials in long-term service is still a concern. In this study, a nondestructive method for ... [more]

Although piezoelectric ceramics are widely used, the structural reliability of these materials in long-term service is still a concern. In this study, a nondestructive method for assessing material strength reliability using partial discharge (PD) tests is proposed. The PD inception electric field and the flexure strength are both controlled by the defects in the ceramics which suggests that the PD test can be an alternative nondestructive method for evaluating the structural reliability of piezoelectric ceramics. PD and four-point flexure tests were carried out on piezoelectric ceramics. The influence of the PD test on samples was investigated by comparing the microstructure and electrical properties before and after the PD test. Samples which were not PD tested were also fractured and compared. It was found that no strength degradation was caused by the PD test. Weibull analysis revealed a correlation between the distribution in values for PD inception electric field and flexure strength. © 2014 The American Ceramic Society.

DOI 10.1111/jace.12875
Citations Scopus - 3Web of Science - 3
2014 Arsecularatne JA, Hoffman M, 'An in vitro study of the microstructure, composition and nanoindentation mechanical properties of remineralizing human dental enamel', Journal of Physics D: Applied Physics, 47 (2014)

This paper describes the results of an in vitro investigation on the interrelations among microstructure, composition and mechanical properties of remineralizing human dental enam... [more]

This paper describes the results of an in vitro investigation on the interrelations among microstructure, composition and mechanical properties of remineralizing human dental enamel. Polished enamel samples have been demineralized for 10 min in an acetic acid solution (at pH 3) followed by remineralization in human saliva for 30 and 120 min. Microstructure variations of sound, demineralized and remineralized enamel samples have been analysed using focused ion beam, scanning electron microscopy and transmission electron microscopy, while their compositions have been analysed using energy dispersive x-ray. Variations in the mechanical properties of enamel samples have been assessed using nanoindentation. The results reveal that, under the selected conditions, only partial remineralization of the softened enamel surface layer occurs where some pores remain unrepaired. As a result, while the nanoindentation elastic modulus shows an improvement following remineralization, hardness does not. © 2014 IOP Publishing Ltd.

DOI 10.1088/0022-3727/47/31/315403
Citations Scopus - 6Web of Science - 6
2014 Borrero-Lopez O, Hoffman M, 'Measurement of fracture strength in brittle thin films', Surface and Coatings Technology, 254 1-10 (2014)

Many coatings and films of interest for engineering applications and microelectromechanical systems (MEMSs) are brittle, and their use under applied stress is ultimately limited b... [more]

Many coatings and films of interest for engineering applications and microelectromechanical systems (MEMSs) are brittle, and their use under applied stress is ultimately limited by fracture. Safe design and material selection therefore require detailed knowledge of the fracture strength. The present work reviews the state-of-the-art in its characterization and analysis. First, we review the experimental methods for strength measurement in small-scale specimens. The more conventional nanomechanical testing of micromachined free-standing films is compared with alternative techniques in which testing is conducted directly on as-deposited films. While the former is preferred for the analysis of MEMS components (e.g.: silicon, silicon oxide, silicon carbide), we argue that the latter is advantageous in order to accurately measure the strength of protective coatings containing residual stress (e.g.: carbon based films; titanium oxide, nitride and nanocomposites; thermal barrier coatings) and of ultra-thin films, and to assess microstructural effects. Given the stochastic nature of brittle fracture, we summarize the fundamentals of Weibull theory for the probabilistic analysis of fracture strength. Special attention is paid to critical variables which affect the measured strength, such as loading geometry and specimen size. Finally, extrapolation from laboratory tests to actual loading configurations during service is briefly discussed. © 2014 Elsevier B.V.

DOI 10.1016/j.surfcoat.2014.05.053
Citations Scopus - 13Web of Science - 13
2014 Xu A, Vodenitcharova T, Kabir K, Flores-Johnson EA, Hoffman M, 'Finite element analysis of indentation of aluminium foam and sandwich panels with aluminium foam core', Materials Science and Engineering A, 599 125-133 (2014)

This paper presents modelling techniques for achieving convergent and accurate solutions in simulating quasi-static indentation of closed-cell aluminium foams and sandwich panels ... [more]

This paper presents modelling techniques for achieving convergent and accurate solutions in simulating quasi-static indentation of closed-cell aluminium foams and sandwich panels with aluminium foam core using the commercial finite-element software ABAQUS/Standard. Various indenters are utilised: hemispherical indenters of 10, 15 and 20. mm diameter, a 16-mm cylindrical flat punch, and a long flat punch. The material parameters are established by comparison with the previous experimental results in uniaxial compression. Experimentally-observed tearing of the cell walls is accounted for in the simulations by introducing element failure and deletion criteria. Stress and strain analysis of the results reveals that foam failure occurs where cell tearing takes place. This occurs at critical tear energy and shear strength, independent of indenter size. The resulting load-displacement curves correlate closely with experimental results. The quasi-static indentation of sandwich panels of aluminium foam cladded with aluminium skins is also simulated for hemispherical indenters of diameter 5-20. mm. Cell tearing does not occur until the point of failure and thus, is not accounted for in the simulations. The effect of the skin strength on the stiffness, strength and energy absorption of the panels is elucidated. A particular emphasis is placed on the material formulation for the foam core which would ensure convergence and reliable predictions. © 2014.

DOI 10.1016/j.msea.2014.01.080
Citations Scopus - 28Web of Science - 28
2014 Hinterstein M, Rouquette J, Haines J, Papet P, Glaum J, Knapp M, et al., 'Structural contribution to the ferroelectric fatigue in lead zirconate titanate ceramics', Physical Review B - Condensed Matter and Materials Physics, 90 (2014)

© 2014 American Physical Society. Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB)... [more]

© 2014 American Physical Society. Many ferroelectric devices are based on doped lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary (MPB), at which the relevant material's properties approach their maximum. Based on a synchrotron x-ray diffraction study of MPB PZT, bulk fatigue is unambiguously found to arise from a less effective field induced tetragonal-to-monoclinic transformation, at which the degradation of the polarization flipping is detected by a less intense and more diffuse anomaly in the atomic displacement parameter of lead. The time dependence of the ferroelectric response on a structural level down to 250 µs confirms this interpretation in the time scale of the piezolectric strain response.

DOI 10.1103/PhysRevB.90.094113
Citations Scopus - 20Web of Science - 20
2014 Gu CF, Toth LS, Hoffman M, 'Twinning effects in a polycrystalline magnesium alloy under cyclic deformation', Acta Materialia, 62 212-224 (2014)

The Taylor-Lin polycrystal elasto-viscoplastic model was employed to simulate the fatigue behavior of a strong basal textured Mg alloy (AZ31) at room temperature. Extensive f10-12... [more]

The Taylor-Lin polycrystal elasto-viscoplastic model was employed to simulate the fatigue behavior of a strong basal textured Mg alloy (AZ31) at room temperature. Extensive f10-12g tensile twinning in a compression-compression cycling mode was shown though no strain hardening occurred in the stress-strain cyclic curves. Using a volume transfer scheme, twinning was simulated where the twin variants were predefined as grains. Parts of the volumes of the mother grains were transferred to the twins by employing the minimum elastic energy criterion for selecting the two least-energy twin variants. Massive detwinning was shown by simulating through transferring parts of the volumes of the twins back to the mother grains. The modeling approach led to fair agreement with experimental twin activity measured by electron backscatter diffraction. The texture changes due to twinning were well reproduced by the model. Additionally, the stress distribution was examined in the polycrystal in the loaded and unloaded (residual) states, separately for the mother and twin grain populations. It has been found that the twins had large residual stresses which deviated in sign and distribution considerably from the residual stresses in the mother grains. This deviation is caused by the different orientations of the twins and the kinematic hardening obtained naturally with crystal plasticity. The crystal plasticity-induced kinematic hardening offers a good interpretation of the large Bauchinger effect observed in low cyclic fatigue of polycrystalline magnesium alloys. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI 10.1016/j.actamat.2013.09.048
Citations Scopus - 36Web of Science - 35
2014 Gu CF, Toth LS, Zhang YD, Hoffman M, 'Unexpected brass-type texture in rolling of ultrafine-grained copper', SCRIPTA MATERIALIA, 92 51-54 (2014)
DOI 10.1016/j.scriptamat.2014.08.012
Citations Scopus - 28Web of Science - 29
2014 Kabir K, Vodenitcharova T, Hoffman M, 'Response of aluminium foam-cored sandwich panels to bending load', Composites Part B: Engineering, 64 24-32 (2014)

The response of aluminium sandwich panels comprising thin foam cores and thin face sheets of low and high yield strength was investigated under three-point bending load. The effec... [more]

The response of aluminium sandwich panels comprising thin foam cores and thin face sheets of low and high yield strength was investigated under three-point bending load. The effect of skin strength, bending span and core thickness on the failure modes and loads was investigated. While the lower strength face sheet is associated with lower failure loads, that decrease is not proportional to the yield strength due to the additional failure mode of face yielding. Theoretical models enabled prediction of the failure loads and elucidated the contribution of each failure mode. Failure maps were subsequently constructed which can be used for the design of foam-cored sandwich panels with very thin face sheets. © 2014 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.compositesb.2014.04.003
Citations Scopus - 31Web of Science - 27
2014 Simons H, Daniels JE, Studer AJ, Jones JL, Hoffman M, 'Measurement and analysis of field-induced crystallographic texture using curved position-sensitive diffraction detectors', Journal of Electroceramics, 32 283-291 (2014)

This paper outlines measurement and analysis methodologies created for determining the structural responses of electroceramics to an electric field. A sample stage is developed to... [more]

This paper outlines measurement and analysis methodologies created for determining the structural responses of electroceramics to an electric field. A sample stage is developed to apply electric fields to ceramic materials at elevated temperatures during neutron diffraction experiments. The tested voltages and temperatures range from -20 kV to +20 kV and room temperature to 200 °C, respectively. The use of the sample environment for measuring the response of ferroelectric ceramics to an electrical stimulus is demonstrated on the instrument Wombat, a monochromatic neutron diffractometer employing a curved positive sensitive detector. Methodologies are proposed to account for the geometrical effects when vector fields are applied to textured materials with angularly dispersive detector geometries. Representative results are presented for the ferroelectric (Bi1/2Na1/2)TiO3- 6%BaTiO3 (BNT-6BT) which show both phase transformation and ferroelectric domain texturing under the application of an electric field. This experimental and analysis approach is well suited for time-resolved measurements such as stroboscopic and in situ studies on a variety of electro-active materials. © 2014 Springer Science+Business Media New York.

DOI 10.1007/s10832-014-9890-8
Citations Scopus - 17Web of Science - 17
2014 Zhang Y, Glaum J, Groh C, Ehmke MC, Blendell JE, Bowman KJ, Hoffman MJ, 'Correlation Between Piezoelectric Properties and Phase Coexistence in (Ba,Ca)(Ti,Zr)O-3 Ceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 97 2885-2891 (2014)
DOI 10.1111/jace.13047
Citations Scopus - 39Web of Science - 39
2014 Chen L, Luo BC, Chan NY, Dai JY, Hoffman M, Li S, Wang DY, 'Enhancement of photovoltaic properties with Nb modified (Bi, Na) TiO3-BaTiO3 ferroelectric ceramics', JOURNAL OF ALLOYS AND COMPOUNDS, 587 339-343 (2014)
DOI 10.1016/j.jallcom.2013.10.207
Citations Scopus - 21Web of Science - 22
2013 Namsar O, Watcharapasorn A, Hoffman M, Glaum J, Jiansirisomboon S, 'Improvement of ferroelectric properties of PZT ceramics by SBT addition', Ferroelectrics, 451 22-29 (2013)

(1-x)PZT-xSBT ceramics were prepared by a solid-state mixed oxide method. Phase characteristics of (1-x)PZT-xSBT ceramics showed a PZT phase and new phase in the compositions with... [more]

(1-x)PZT-xSBT ceramics were prepared by a solid-state mixed oxide method. Phase characteristics of (1-x)PZT-xSBT ceramics showed a PZT phase and new phase in the compositions with 0.1 = x = 0.3, while a mainly new phase was observed in the compositionwith x=0.5. The tetragonality (c/a) of PZT phase decreasedwith increasing in SBT content up to x = 0.3. SEM micrographs of the sample surface showed equiaxed grains of the PZT phase and irregularly-shaped grains of the new phase in samples with 0.1 = x = 0.3. The 0.5PZT-0.5SBT sample showed mainly irregularly-shaped grains of the new phase. The ferroelectric properties of these samples showed that the addition of small amounts of SBT (x = 0.1) into PZT increased the remanent polarization. Copyright © 2013 Taylor & Francis Group, LLC.

DOI 10.1080/00150193.2013.838882
Citations Scopus - 1Web of Science - 1
2013 Kemal I, Whittle A, Burford R, Vodenitcharova T, Hoffman M, 'Toughening of unmodified polyvinylchloride through the addition of nanoparticulate calcium carbonate and titanate coupling agent', Journal of Applied Polymer Science, 127 2339-2353 (2013)

PVC/CaCO 3 polymer nanocomposites of differing compositions were produced using a two-roll mill and compression molding. In all formulations, 0.6 phr of titanate was incorporated ... [more]

PVC/CaCO 3 polymer nanocomposites of differing compositions were produced using a two-roll mill and compression molding. In all formulations, 0.6 phr of titanate was incorporated to assist dispersion during processing. The morphology was observed using transmission electron microscopy, and the static and dynamic mechanical and fracture properties were determined. Fracture toughness examination was performed according to strain energy release test method. The presence of nanometer-sized CaCO 3 particles led to a slight decrease in the tensile strength but improved the impact energy absorption, storage modulus, and fracture toughness. The use of titanate coupling agent softened the polymer matrix and reduced the matrix's modulus. Fracture surface examinations by scanning electron microscopy showed that the coupling agent improved particle-matrix bonding and inhibited void formation around the particles. Finite element analysis suggested that the improved particle-matrix bonding reduced the matrix's plasticity around the particles, which decreased the toughening efficiency of the composites. © 2012 Wiley Periodicals, Inc.

DOI 10.1002/app.37774
Citations Scopus - 19Web of Science - 20
2013 Glaum J, Simons H, Acosta M, Hoffman M, 'Tailoring the Piezoelectric and Relaxor Properties of (Bi1/2Na1/2)TiO3-BaTiO3 via Zirconium Doping', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 96 2881-2886 (2013)
DOI 10.1111/jace.12405
Citations Scopus - 30Web of Science - 28
2013 Ehmke MC, Glaum J, Hoffman M, Blendell JE, Bowman KJ, 'In Situ X-ray Diffraction of Biased Ferroelastic Switching in Tetragonal Lead-free (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 Piezoelectrics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 96 2913-2920 (2013)
DOI 10.1111/jace.12424
Citations Scopus - 35Web of Science - 34
2013 Ehmke MC, Glaum J, Hoffman M, Blendell JE, Bowman KJ, 'The Effect of Electric Poling on the Performance of Lead-Free (1-x)Ba(Zr0.2Ti0.8)O-3-x(Ba0.7Ca0.3)TiO3 Piezoceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 96 3805-3811 (2013)
DOI 10.1111/jace.12586
Citations Scopus - 27Web of Science - 26
2013 Simons H, Daniels JE, Glaum J, Studer AJ, Jones JL, Hoffman M, 'Origin of large recoverable strain in 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO(3) near the ferroelectric-relaxor transition', APPLIED PHYSICS LETTERS, 102 (2013)
DOI 10.1063/1.4790285
Citations Scopus - 45Web of Science - 47
2013 Simons H, Daniels JE, Glaum J, Studer AJ, Jones JL, Hoffman M, 'Origin of large recoverable strain in 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO(3) near the ferroelectric-relaxor transition (vol 102, 062902, 2013)', APPLIED PHYSICS LETTERS, 102 (2013)
DOI 10.1063/1.4795239
Citations Scopus - 3
2012 Wang BL, Hoffman M, Yu AB, 'Buckling analysis of embedded nanotubes using gradient continuum theory', Mechanics of Materials, 45 52-60 (2012)

The buckling of nanotubes embedded in an elastic matrix is modeled within the framework of Timoshenko beams. Both a stress gradient and a strain gradient approach are considered. ... [more]

The buckling of nanotubes embedded in an elastic matrix is modeled within the framework of Timoshenko beams. Both a stress gradient and a strain gradient approach are considered. The energy variational approach is adopted to obtain the critical buckling loads. The dependences of the buckling load on the nonlocal parameter, the stiffness of the surrounding elastic matrix, and the transverse shear stiffness of the nanotubes are obtained. The results show a significant dependence of critical buckling load on the nonlocal parameter and the stiffness of the surround matrix. The Euler beam model, which neglects the shear stiffness of the nanotubes, over-predicts the critical buckling load. It is also found that the strain gradient model provides the lower bound and the stress gradient model provides the upper bound for the critical buckling load of nanotubes. In addition to mechanical buckling, thermally induced buckling of the nanotubes embedded in an elastic matrix is also studied. All results are expressed in closed-form and therefore are easy to use by materials scientists and engineers for the design of nanotubes and their composites. © 2011 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.mechmat.2011.10.003
Citations Scopus - 23Web of Science - 24
2012 Wattanasakulpong N, Gangadhara Prusty B, Kelly DW, Hoffman M, 'Free vibration analysis of layered functionally graded beams with experimental validation', Materials and Design, 36 182-190 (2012)

An improved third order shear deformation theory is employed to formulate a governing equation for predicting free vibration of layered functionally graded beams. The Ritz method ... [more]

An improved third order shear deformation theory is employed to formulate a governing equation for predicting free vibration of layered functionally graded beams. The Ritz method is adopted to solve the governing equation for various types of boundary conditions and the frequency results are validated by some available and experimental results. A multi-step sequential infiltration technique is used to fabricate the layered functionally graded beams for vibration testing. For the first time, a simple mathematical model, based on a power law distribution, is introduced to approximate material volume fraction of the layered beams. The details of layered beam fabrication according to the infiltration technique, microstructure and volume fraction analysis as well as vibration experimental set up are included and described in this investigation. Aspects which affect natural frequencies, such as material compositions, thickness ratio, and boundary conditions, are then taken into consideration. The impact on frequency of added mass is presented and discussed. © 2011 Elsevier Ltd.

DOI 10.1016/j.matdes.2011.10.049
Citations Scopus - 151Web of Science - 141
2012 Vodenitcharova T, Kabir K, Hoffman M, 'Indentation of metallic foam core sandwich panels with soft aluminium face sheets', Materials Science and Engineering A, 558 175-185 (2012)

A closed-form analytical model is presented for the deformation and fracture behaviour of sandwich panels with ductile foam cores and low yield-strength face sheets when subjected... [more]

A closed-form analytical model is presented for the deformation and fracture behaviour of sandwich panels with ductile foam cores and low yield-strength face sheets when subjected to quasi-static indentation with hemispherical indenters of various diameters and compared with an extensive experimental investigation. The aim is to predict the indentation strength and the influence of the indenter size on it. The face sheet is assumed an isotropic thin sheet undergoing large tensile deformation and bonded to a rigid-plastic foundation. The indentation strength of the sandwich panel is presented as a superposition of the force contributions of the skin, the foam core and the interfacial shear at the skin-foam interface at the point of skin fracture. To validate the model, sandwich panels with 0.32. mm thick sheets of AA 1100-O aluminium alloy and aluminium closed-cell foam core are quasi-statically indented with spherical indenters of 10, 15 and 20. mm diameters. It is established that failure of the sandwich panels is governed by radial skin fracture, and that the indenter size and the foam resistance greatly influence the indentation response as larger indenters are associated with higher failure loads. A simple parameter for system failure is ascertained, the subtended angle at the indenter-skin contact, which is dependent on the product of the indenter radius and the foam compressive strength. The developed model closely predicts the experimental load-displacement history and the failure loads and may be applied to any thin soft sheets bonded to a rigid-plastic foundation, and thus, to other sandwich constructions of similar constituents. © 2012 Elsevier B.V.

DOI 10.1016/j.msea.2012.07.108
Citations Scopus - 11Web of Science - 11
2012 Vodenitcharova T, Borrero-López O, Hoffman M, 'Mechanics prediction of the fracture pattern on scratching wafers of single crystal silicon', Acta Materialia, 60 4448-4460 (2012)

The effect of anisotropy on the response and fracture pattern on scratching {1 0 0} and {1 1 1} single crystal silicon wafers in two characteristic directions, i.e. &lt;1 0 0&gt; ... [more]

The effect of anisotropy on the response and fracture pattern on scratching {1 0 0} and {1 1 1} single crystal silicon wafers in two characteristic directions, i.e. <1 0 0> and <1 1 0> in a {1 0 0} wafer, and <1 1 0> and <1 1 2> in a {1 1 1} wafer, respectively, was studied. Predictions of the locations of the onset of fracture, as well as the fracture patterns on the wafer surfaces, were obtained applying a "minimum crack length" criterion assisted by numerical determination of the stress states using the finite element method. It was found that the first crack appears on the {1 1 1} or {1 1 0} cleavage plane. The <1 1 2> scratching direction on the {1 1 1} wafer is the weakest among the four directions studied, since it provides the highest resolved tensile stress and the shortest initial defect for crack propagation. The <1 0 0> scratching direction in the {1 0 0} wafer appears to be strongest. Experiments validated the approach and also showed a higher reliability in the {1 0 0}<1 0 0> and {1 1 1}<1 1 0> directions. The methodology used in this manuscript can be applied to the determination of fracture patterns in other single crystal materials, under scratching or other mechanical loading conditions. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI 10.1016/j.actamat.2012.04.040
Citations Scopus - 14Web of Science - 13
2012 Arsecularatne JA, Hoffman M, 'Ceramic-like wear behaviour of human dental enamel', Journal of the Mechanical Behavior of Biomedical Materials, 8 47-57 (2012)

This paper reports a transmission electron microscopy (TEM) analysis of subsurfaces of enamel specimens following in vitro reciprocating wear tests with an enamel cusp sliding on ... [more]

This paper reports a transmission electron microscopy (TEM) analysis of subsurfaces of enamel specimens following in vitro reciprocating wear tests with an enamel cusp sliding on a flat enamel specimen under hydrated conditions. The obtained results show that crack formation occurred in the wear scar subsurface. The path followed by these cracks seems to be dictated either by the histological structure of enamel or by the contact stress field. Moreover, the analysis of a set of enamel wear results obtained from the literature and application of fracture-based models, originally developed for ceramics, correlate well, confirming the similar wear processes taking place in these materials. This analysis also reveals a marked influence of coefficient of friction on the enamel wear rate: for a higher coefficient of friction value, enamel wear can be severe even under forces generated during normal operation of teeth. © 2011 Elsevier Ltd.

DOI 10.1016/j.jmbbm.2011.12.002
Citations Scopus - 22Web of Science - 21
2012 Dittmer R, Anton E-M, Jo W, Simons H, Daniels JE, Hoffman M, et al., 'A High-Temperature-Capacitor Dielectric Based on K0.5Na0.5NbO3-Modified Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 95 3519-3524 (2012)
DOI 10.1111/j.1551-2916.2012.05321.x
Citations Scopus - 90Web of Science - 85
2012 Simons H, Glaum J, Daniels JE, Studer AJ, Liess A, Roedel J, Hoffman M, 'Domain fragmentation during cyclic fatigue in 94%(Bi1/2Na1/2)TiO3-6%BaTiO3', JOURNAL OF APPLIED PHYSICS, 112 (2012)
DOI 10.1063/1.4745900
Citations Scopus - 29Web of Science - 29
2012 Ehmke MC, Daniels J, Glaum J, Hoffman M, Blendell JE, Bowman KJ, 'Reduction of the piezoelectric performance in lead-free (1-x)Ba(Zr0.2Ti0.8)O-3-x(Ba0.7Ca0.3)TiO3 piezoceramics under uniaxial compressive stress', JOURNAL OF APPLIED PHYSICS, 112 (2012)
DOI 10.1063/1.4768273
Citations Scopus - 33Web of Science - 34
2011 Luo Z, Glaum J, Granzow T, Jo W, Dittmer R, Hoffman M, Rödel J, 'Bipolar and unipolar fatigue of ferroelectric BNT-based lead-free piezoceramics', Journal of the American Ceramic Society, 94 529-535 (2011)

The bipolar and unipolar fatigue behavior of the lead-free piezo- and ferroelectric 0.94Bi1/2Na1/2TiO3-0.06BaTiO 3 (94BNT-6BT) was investigated. To obtain a complete profile of th... [more]

The bipolar and unipolar fatigue behavior of the lead-free piezo- and ferroelectric 0.94Bi1/2Na1/2TiO3-0.06BaTiO 3 (94BNT-6BT) was investigated. To obtain a complete profile of the fatigue behavior, both large-signal (polarization, strain) and small-signal (d33, É33) properties were measured at room temperature. The results indicate that the material suffers a significant degradation in both large- and small-signal properties after cycling, with most of the fatigue occurring in the first 104 cycles of the fatigue test. © 2010 The American Ceramic Society.

DOI 10.1111/j.1551-2916.2010.04101.x
Citations Scopus - 65Web of Science - 66
2011 Pojprapai S, Simons H, Studer AJ, Luo Z, Hoffman M, 'Temperature dependence on domain switching behavior in lead zirconate titanate under electrical load via in situ neutron diffraction', Journal of the American Ceramic Society, 94 3202-3205 (2011)

The influence of temperature on the kinetics of domain switching in lead zirconate titanate was investigated by using in situ neutron diffraction. Samples were electrically loaded... [more]

The influence of temperature on the kinetics of domain switching in lead zirconate titanate was investigated by using in situ neutron diffraction. Samples were electrically loaded to 1 kV/mm at 30°C, 125°C, and 175°C, after which the diffracted patterns in the on- and off-state were compared. The results demonstrated that the degree of domain switching increases with increased temperature. Corroboration with hysteresis measurements showed that while the coercive field decreases with increasing temperature, the degree of saturation increased significantly. According to Merz's model, it is therefore apparent that, due to increased switching rate at high temperature, domain switchability increases with temperature. © 2011 The American Ceramic Society.

DOI 10.1111/j.1551-2916.2011.04783.x
Citations Scopus - 6Web of Science - 6
2011 Arsecularatne JA, Hoffman M, O'Kelly K, Payraudeau N, 'FIB tomographic analysis of subsurface indentation crack interactions with pores in alumina', Journal of the American Ceramic Society, 94 4017-4024 (2011)

This article describes a study involving three-dimensional FIB tomographic characterization of Vickers microindentation sites in an alumina material containing pores. The study wa... [more]

This article describes a study involving three-dimensional FIB tomographic characterization of Vickers microindentation sites in an alumina material containing pores. The study was carried out using a dual beam FIB instrument for loads in the range 50-200 g. The results obtained show that this technique can be used to obtain 3-D distributions of indentation-generated cracks. Although, compared to a dense material, presence of pores in alumina reduced the ability to generate and/or propagate radial cracks, the significant probability of crack-pore interactions indicates that pores assist in the generation/ propagation lateral cracks. The subsurface images show that pores act as sites for crack initiation and/or assist in crack propagation. In addition, a clearly reduced ability to generate and/or propagate radial cracks has been noted. However, considering that FIB tomography is destructive and invasive, microstructural changes seem to have occurred during the process and consequently it is not possible to identify all the generated cracks. Moreover, propagation of some of the cracks also occurred due to material removal in FIB milling. © 2011 The American Ceramic Society.

DOI 10.1111/j.1551-2916.2011.04661.x
Citations Scopus - 3Web of Science - 3
2011 Dayal P, Quadir MZ, Kong C, Savvides N, Hoffman M, 'Transition from dislocation controlled plasticity to grain boundary mediated shear in nanolayered aluminum/palladium thin films', THIN SOLID FILMS, 519 3213-3220 (2011)
DOI 10.1016/j.tsf.2010.12.112
Citations Scopus - 25Web of Science - 21
2011 Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'Mechanical properties and scratch resistance of filtered-arc-deposited titanium oxide thin films on glass', Thin Solid Films, 519 7925-7931 (2011)

The mechanical properties and the scratch resistance of titanium oxide (TiO2) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and ana... [more]

The mechanical properties and the scratch resistance of titanium oxide (TiO2) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and anatase) and amorphous structures, were deposited by the filtered cathodic vacuum arc deposition technique on glass, and characterized by means of nanoindentation and scratch tests. The different damage modes (arc-like, longitudinal and channel cracks in the crystalline films; Hertzian cracks in the amorphous film) were assessed by means of optical and focused ion beam microscopy. In all cases, the deposition of the TiO 2 film improved the contact-mechanical properties of uncoated glass. Crystalline films were found to possess a better combination of mechanical properties (i.e. elastic modulus up to 221 GPa, hardness up to 21 GPa, and fracture strength up to 3.6 GPa) than the amorphous film. However, under cyclic sliding contact above the critical fracture load, the amorphous film was found to withstand a higher number of cycles. The results are expected to provide useful insight for the design of optical coatings with improved contact-damage resistance. © 2011 Elsevier B.V. All rights reseved.

DOI 10.1016/j.tsf.2011.07.011
Citations Scopus - 19Web of Science - 15
2011 Zavgorodniy AV, Borrero-López O, Hoffman M, Legeros RZ, Rohanizadeh R, 'Characterization of the chemically deposited hydroxyapatite coating on a titanium substrate', Journal of Materials Science: Materials in Medicine, 22 1-9 (2011)

Bioactive hydroxyapatite (HA) coating on titanium (Ti) implant can be used as a drug delivery device. A controlled release of drug around the implant requires the incorporation of... [more]

Bioactive hydroxyapatite (HA) coating on titanium (Ti) implant can be used as a drug delivery device. A controlled release of drug around the implant requires the incorporation of drug into the coating material during the coating process. HA coating was prepared using a two-step procedure in conditions suitable for simultaneous incorporation of the protein-based drug into the coating material. Monetite coating was deposited on Ti substrate in acidic condition followed by the transformation of the monetite coating to HA. X-ray diffraction (XRD) confirmed the formation of the monetite phase at the first step of the coating preparation, which was transformed into HA at the second step. Fourier transform infrared spectroscopy demonstrated typical bands of a crystallized carbonated HA with A- and B-type substitution, which was confirmed by the XRD refinement of the structural parameters. Scanning electron microscope was used to observe the morphology of monetite and HA coatings. Adhesion of the coatings was measured using a scratch tester. The critical shearing stress was found to be 84.20 ± 1.27 MPa for the monetite coating, and 44.40 ± 2.39 MPa for the HA coating. © 2010 Springer Science+Business Media, LLC.

DOI 10.1007/s10856-010-4179-1
Citations Scopus - 21Web of Science - 20
2011 Pojprapai (Imlao) S, Jones JL, Vodenitcharova T, Bernier JV, Hoffman M, 'Investigation of the domain switching zone near a crack tip in pre-poled lead zirconate titanate ceramic via in situ X-ray diffraction', SCRIPTA MATERIALIA, 64 1-4 (2011)
DOI 10.1016/j.scriptamat.2010.08.053
Citations Scopus - 13Web of Science - 13
2011 Zavgorodniy AV, Borrero-López O, Hoffman M, Legeros RZ, Rohanizadeh R, 'Mechanical stability of two-step chemically deposited hydroxyapatite coating on Ti substrate: Effects of various surface pretreatments', Journal of Biomedical Materials Research - Part B Applied Biomaterials, 99 B 58-69 (2011)

The success of implants in orthopaedic and dental load-bearing applications crucially depends on the initial biological fixation of implants in surrounding bone tissues. Using hyd... [more]

The success of implants in orthopaedic and dental load-bearing applications crucially depends on the initial biological fixation of implants in surrounding bone tissues. Using hydroxyapatite (HA) coating on Ti implant as carrier for bone morphogenetic proteins (BMPs) may promote the osteointegration of implants; therefore, reduce the risk of implant failure. The goal of this study was to develop an HA coating method in conditions allowing the incorporation of protein-based drugs into the coating materials, while achieving a mechanical stable coating on Ti implant. HA coatings were deposited on six different groups of Ti surfaces: control (no pretreatment), pretreated with alkali, acid, heat at 800°C, grit blasted with Al 2O 3, and grit blasted followed by heat treatment. HA coating was prepared using a two-step procedure. First step was the chemical deposition of a monetite coating on Ti substrate in acidic condition at 75°C and the second step was the hydrolysis of the monetite coating to HA. Coatings were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The roughness of substrates and coatings was measured using profilometry technique. The mechanical stability of the coatings deposited on the pretreated substrates was assessed using scratch test. The coatings deposited on the grit-blasted Ti surface demonstrated superior adhesive properties with critical shearing stress 131.6 ± 0.2 MPa. Copyright © 2011 Wiley Periodicals, Inc.

DOI 10.1002/jbm.b.31872
Citations Scopus - 24Web of Science - 18
2011 Hoo RP, Fratzl P, Daniels JE, Dunlop JWC, Honkimäki V, Hoffman M, 'Cooperation of length scales and orientations in the deformation of bovine bone', Acta Biomaterialia, 7 2943-2951 (2011)

Bone has a complex hierarchical structure. Combined wide angle X-ray diffraction and small angle X-ray scattering were used together with in situ tensile testing to investigate th... [more]

Bone has a complex hierarchical structure. Combined wide angle X-ray diffraction and small angle X-ray scattering were used together with in situ tensile testing to investigate the deformation and failure mechanisms of bovine cortical bone at three material levels: (1) the atomic level, corresponding to the mineral crystal phase; (2) the nano level, corresponding to the collagen fibrils; (3) the macroscopic level. It was found that deformation was linear at all three levels up to a strain of 0.2% in the longitudinal tensile direction. At this critical strain a sudden 50% decrease in the fibrillar and mineral strains was observed. This suggests the presence of partial local damage that leads to inhomogeneous strain distributions within the probed gauge volume. This also gives rise to diffraction peak broadening in the mineral phase, as well as strain relaxation at the nanoscale. Above the critical strain the longitudinally oriented strains below the nanoscale remained constant at a reduced level until failure. This suggests that the lateral orientation of the nanostructures toughens the bone, while a higher material level dominated the subsequent deformation process, either by sliding between the lamellar layers or by the growth of microcracks. Analysis of the diffraction data also shows that the bone has compressive residual stress in the crystal phase. A better understanding of the basic mechanics of the hierarchical bone structure could be the basis to enhance research in biomimetics, developing new advanced materials, and to find solutions for orthopedic problems.

DOI 10.1016/j.actbio.2011.02.017
Citations Scopus - 22Web of Science - 21
2011 Luo Z, Granzow T, Glaum J, Jo W, Roedel J, Hoffman M, 'Effect of Ferroelectric Long-Range Order on the Unipolar and Bipolar Electric Fatigue in Bi1/2Na1/2TiO3-Based Lead-Free Piezoceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94 3927-3933 (2011)
DOI 10.1111/j.1551-2916.2011.04605.x
Citations Scopus - 65Web of Science - 63
2011 Simons H, Daniels J, Jo W, Dittmer R, Studer A, Avdeev M, et al., 'Electric-field-induced strain mechanisms in lead-free 94%(Bi1/2Na1/2)TiO3-6%BaTiO3', APPLIED PHYSICS LETTERS, 98 (2011)
DOI 10.1063/1.3557049
Citations Scopus - 112Web of Science - 112
2010 Samat N, Burford R, Whittle A, Hoffman M, 'The effects of water and frequency on fatigue crack growth rate in modified and unmodified polyvinyl chloride', Polymer Engineering and Science, 50 352-364 (2010)

A study of the influence of water environments on the cyclic fatigue crack behavior of polyvinyl chloride (PVC), with (PVC-M) and without (PVC-U) chlorinated polyethylene (CPE) im... [more]

A study of the influence of water environments on the cyclic fatigue crack behavior of polyvinyl chloride (PVC), with (PVC-M) and without (PVC-U) chlorinated polyethylene (CPE) impact modifier was undertaken and compared with corresponding results in air. Two frequencies of 1 and 7 Hz were applied to assess the influence of frequency on the fatigue behavior; a higher fatigue resistance and threshold were obtained with increasing frequency. This trend is more significant in water. However, in this environment, the fatigue resistance deteriorated under conditions of higher stress intensity factor amplitude (¿K) and frequency. The fatigue properties of PVC-U are the most affected by the presence of water, particularly at low frequency and higher ¿K. Examination of the fracture surface showed the interaction of water molecules and the PVC matrix with the formation of (1) a nodular structure, close to the fatigue threshold and (2) plasticized structures at high ¿K, which are associated with a greater threshold value and fatigue resistance. The absorption of the water retarded the fibrillation of craze and caused crack blunting effects. Water functions as a plasticizer, particularly at high ¿K, through the formation of the plasticized structures. Results are compared with those observed from an in-service failure. POLYM. ENG. SCI., 50:352-364, 2010. Copyright © 2009 Society of Plastics Engineers.

DOI 10.1002/pen.21547
Citations Scopus - 2Web of Science - 2
2010 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Effect of coating thickness on the deformation behaviour of diamond-like carbon-silicon system', Thin Solid Films, 518 2021-2028 (2010)

The effect of coating thickness on the deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates was investigated. Following nanoindentation of a 0.6 µm th... [more]

The effect of coating thickness on the deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates was investigated. Following nanoindentation of a 0.6 µm thick DLC coating, the subsurface microstructures were characterized and the data was compared to prior studies on a similar, but thicker coating. Indentation resulted in localized plastic compression in the coating without any through-thickness cracking. It was shown that the discontinuities in the load-displacement curves appeared at lower loads for the thinner coating. Accordingly, the silicon substrate exhibited cracking, plastic deformation and phase transformation at significantly lower loads than in the case of the thicker coating. Further, the widths, parallel to the interface, over which slip and the phase transformation zone are spread out in the substrate, was found to increase with the thickness of the coating. The mechanism responsible for the first pop-in was found to change from phase transformation in uncoated silicon to dislocation nucleation in the presence of the coating. Crown Copyright © 2009.

DOI 10.1016/j.tsf.2009.08.041
Citations Scopus - 12Web of Science - 7
2010 Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'The use of the scratch test to measure the fracture strength of brittle thin films', Thin Solid Films, 518 4911-4917 (2010)

The feasibility of the use of the scratch test to measure the fracture strength of brittle thin films has been proved. In particular, amorphous diamond-like carbon (DLC), SiC and ... [more]

The feasibility of the use of the scratch test to measure the fracture strength of brittle thin films has been proved. In particular, amorphous diamond-like carbon (DLC), SiC and TiO2 films deposited on a soda-lime glass substrate, in which damage initiated on the film surface in the form of partial cone cracks, have been considered. Optical inspection of the scratch tracks allowed the normal and lateral force at the point of fracture to be determined. The critical values were subsequently used to calculate the fracture strength. The great advantage of this method is that it allows the contribution of surface defects to strength to be obtained. Weibull analysis of the strength data was carried out, showing that the SiC film possess higher strength and reliability compared to DLC and TiO2 films. © 2010 Elsevier B.V. All rights reserved.

DOI 10.1016/j.tsf.2010.04.015
Citations Scopus - 21Web of Science - 17
2010 Weidner M, Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'Effect of substrate roughness on the contact damage of thin brittle films on brittle substrates', Thin Solid Films, 518 5242-5248 (2010)

The effect of substrate and surface roughness on the contact fracture of diamond-like carbon coatings on brittle soda-lime glass substrates has been investigated. The average surf... [more]

The effect of substrate and surface roughness on the contact fracture of diamond-like carbon coatings on brittle soda-lime glass substrates has been investigated. The average surface roughness (Ra) of the examined samples ranged from 15 nm to 571 nm. Contact damage was simulated by means of spherical nanoindentation, and fracture was subsequently assessed by focused ion beam microscopy. It was found that, in the absence of sub-surface damage in the substrate, fracture occurs in the coating in the form of radial, and ring/cone cracks during loading, and lateral cracks during unloading. Increasing the surface roughness results in a decrease in the critical load for crack initiation during loading, and in the suppression of fracture modes during unloading from high loads. When sub-surface damage (lateral cracks) is present in the substrate, severe spalling takes place during loading, causing a large discontinuity in the load-displacement curve. The results have implications concerning the design of damage-tolerant coated systems consisting of a brittle film on a brittle substrate. © 2010 Elsevier B.V.

DOI 10.1016/j.tsf.2010.04.039
Citations Scopus - 4Web of Science - 4
2010 Ma LW, Cairney JM, Hoffman MJ, Munroe PR, 'Effect of coating thickness on the deformation mechanisms in PVD TiN-coated steel', Surface and Coatings Technology, 204 1764-1773 (2010)

The deformation mechanisms of a range of TiN coatings with different thicknesses, deposited on a V820 steel substrate following nanoindentation were characterized using focused io... [more]

The deformation mechanisms of a range of TiN coatings with different thicknesses, deposited on a V820 steel substrate following nanoindentation were characterized using focused ion beam (FIB) cross-sectioning and imaging, as well as cross-sectional transmission electron microscopy (TEM) of the indented region. Four TiN coatings were examined, including a cathodic arc evaporation (CAE) coating with a thickness of ~ 0.7 µm and low voltage electron beam (LVEB) evaporation coatings with thicknesses of ~ 2.0, ~ 3.7 and ~ 4.0 µm. Based on a model developed by Xie et al., the intercolumnar shear stresses were calculated to be approximately 2.20, 3.05, 3.50 and 3.55 GPa in the ~ 0.7, ~ 2.0, ~ 3.7 and ~ 4.0 µm thick TiN coatings respectively, that is, increasing as the coating thickness increases. Columnar cracking and shear steps at the coating/substrate interface were observed more frequently in the thinner TiN coatings indicated that these coatings deformed predominantly by shear along the columnar grain boundaries. In contrast, inclined cracking was the more dominant fracture type in the thicker TiN coatings. It is suggested that increased grain boundary strength occurs together with a lack of direct crack path along the grain boundaries through the thicker coatings due to the more equiaxed grain structure. Clearly, the grain structure and/or thickness of the TiN coating play a highly significant role in the deformation mechanisms. © 2009 Elsevier B.V. All rights reserved.

DOI 10.1016/j.surfcoat.2009.11.008
Citations Scopus - 30Web of Science - 26
2010 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Correlation of nanoindentation-induced deformation microstructures In diamondlike carbon coatings on silicon substrates with simulation studies', Journal of Materials Research, 25 910-920 (2010)

The effect of the presence of diamondlike carbon coatings deposited on (100) Si substrates on the deformation mechanisms operating in the silicon substrate during contact loading ... [more]

The effect of the presence of diamondlike carbon coatings deposited on (100) Si substrates on the deformation mechanisms operating in the silicon substrate during contact loading have been investigated by both cross-sectional transmission electron microscopy and modeling of the stresses generated beneath the indenter tip. The observed subsurface microstructures were correlated to the Tresca shear stress and the hydrostatic stress generated in the silicon substrate beneath the indenter tip. The presence of the coating altered the stresses generated in the substrate, and changed the deformation mechanism from one of principally phase transformation in uncoatcd Si to predominantly dislocation motion in the silicon substrate for the diamondlike C-Si system. The magnitude and distribution of the shear and hydrostatic stresses in the substrate were found to depend on both the indentation load and the thickness of the coating. Furthermore, the observed width of deformation, parallel to the interface, which was found to increase with coating thickness, was correlated to the wider distribution of the Tresca shear stress in the substrate brought about by the presence of the coating. © 2010 Materials Research Society.

DOI 10.1557/jmr.2010.0131
Citations Scopus - 2Web of Science - 2
2010 Vodenitcharova T, Idris M, Hoffman M, 'Experimental and analytical study on the deformation response of closed-cell Al foam panels to local contact damage-Mechanical properties extraction', Materials Science and Engineering A, 527 6033-6045 (2010)

The present paper studies the deformation response of closed-cell aluminium foam panels (ALPORAS brand) to local contact damage, experimentally simulated by indentation tests with... [more]

The present paper studies the deformation response of closed-cell aluminium foam panels (ALPORAS brand) to local contact damage, experimentally simulated by indentation tests with indenters of various shapes and sizes. The foam density varies between 0.184g/cm3 and 0.351g/cm3; panels of various thicknesses are also considered. Analytical models are developed to estimate the crushing force, the tearing resistance, and the shearing resistance in indentation with cylindrical and spherical indenters. Of particular interest are the failure mechanisms, the foam ligament tear energy and the foam shear strength in all indentation types. The tear energy, as well as the shear strength, is deduced by fitting the experimental load-displacement curves and using the developed analytical models. The influence of the panel thickness, indenter shape and size, and foam microstructure on the deformation mechanisms and material properties is also discussed. © 2010 Elsevier B.V.

DOI 10.1016/j.msea.2010.06.003
Citations Scopus - 7Web of Science - 6
2010 Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'Substrate effects on the mechanical properties and contact damage of diamond-like carbon thin films', Diamond and Related Materials, 19 1273-1280 (2010)

Substrate effects on the mechanical properties and contact damage of diamond-like carbon (DLC) films have been investigated. To that end, a DLC film of 1 µm thickness was deposite... [more]

Substrate effects on the mechanical properties and contact damage of diamond-like carbon (DLC) films have been investigated. To that end, a DLC film of 1 µm thickness was deposited on two different substrates: soda-lime glass (compliant and soft), and single-crystal silicon (stiff and hard). The elastic modulus and hardness were measured by means of nanoindentation. Quasi-static and sliding contact configurations were simulated by means of ultra-micro indentation, and surface and cross-sectional damage were assessed using a focused ion beam (FIB) miller. It was found that a compliant and soft substrate enhances crack initiation on the film surface in the form of ring/cone cracks. On the other hand, a stiff and hard substrate delays crack initiation in the film, but is more susceptible to fracture in the form of median and lateral cracks due to increased brittleness. The results have implications for the reliability of DLC-coated systems. © 2010 Elsevier B.V. All rights reserved.

DOI 10.1016/j.diamond.2010.06.004
Citations Scopus - 18Web of Science - 13
2010 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Nanoindentation-induced deformation behaviour of tetrahedral amorphous carbon coating deposited by filtered cathodic vacuum arc', Diamond and Related Materials, 19 1423-1430 (2010)

The nanoindentation-induced deformation behaviour of a ta-C (tetrahedral amorphous carbon) coating deposited on to a silicon substrate by a filtered vacuum cathodic vapour arc tec... [more]

The nanoindentation-induced deformation behaviour of a ta-C (tetrahedral amorphous carbon) coating deposited on to a silicon substrate by a filtered vacuum cathodic vapour arc technique was investigated. The 0.17-µm-thick ta-C coating was subjected to nanoindentation with a spherical indenter and the residual indents were examined by cross-sectional transmission electron microscopy. The hard (~ 30 GPa) ta-C coatings exhibited very little localized plastic compression, unlike the softer amorphous carbon coatings deposited by plasma-assisted chemical vapour deposition. However, neither through-thickness cracks nor delamination was observed in the coating for the loads studied. Rather, the silicon substrate exhibited plastic deformation for indentation loads as low as 10 mN and at higher loads it showed evidence of both phase transformation and cracking. These microstructural features were correlated to the observed discontinuities in the load-displacement curves. Further, it was observed that even a very thin coating can modify the primary deformation mechanism from phase transformation in uncoated Si to predominantly plastic deformation in the underlying substrate. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

DOI 10.1016/j.diamond.2010.08.014
Citations Scopus - 4Web of Science - 4
2010 Pojprapai(Imlao) S, Luo Z, Clausen B, Vogel SC, Brown DW, Russel J, Hoffman M, 'Dynamic processes of domain switching in lead zirconate titanate under cyclic mechanical loading by in situ neutron diffraction', Acta Materialia, 58 1897-1908 (2010)

The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure... [more]

The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure of ferroelectric devices. In this work the dynamic properties of domain reorientation are studied. In situ time-of-flight neutron diffraction is used to probe the evolution of ferroelastic domain texture under mechanical cyclic loading in bulk lead zirconate titanate ceramics. The high sensitivity of neutron diffraction to lattice strain is exploited to precisely analyze the change of domain texture and strain through a full-pattern Rietveld method. These results are then used to construct a viscoelastic model, which explains the correlation between macroscopic phenomena (i.e. creep and recovered deformation) and microscopic dynamic behavior (i.e. ferroelastic switching, lattice strain). © 2009 Acta Materialia Inc.

DOI 10.1016/j.actamat.2009.11.026
Citations Scopus - 10Web of Science - 8
2010 Borrero-López O, Vodenitcharova T, Hoffman M, 'Anisotropy effects on the reliability of single-crystal silicon', Scripta Materialia, 63 997-1000 (2010)

Anisotropy effects on the reliability of single-crystal silicon were investigated by means of scratch tests along [1 1 0] and [1 0 0] crystallographic directions. It was found tha... [more]

Anisotropy effects on the reliability of single-crystal silicon were investigated by means of scratch tests along [1 1 0] and [1 0 0] crystallographic directions. It was found that fracture (partial cone cracks) starts along favoured {1 1 0} and {1 1 1} cleavage planes, with crack orientation varying upon the scratching direction. Moreover, the [1 0 0] direction was found to be twice as reliable as the [1 1 0] direction. Stress and phase analyses were carried out to explain this effect, which has implications for the design of silicon-based devices. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI 10.1016/j.scriptamat.2010.07.024
Citations Scopus - 13Web of Science - 10
2010 Wang BL, Hoffman M, 'Closed form solution for a line inclusion in magnetoelectroelastic media', International Journal of Applied Electromagnetics and Mechanics, 34 119-129 (2010)

This paper studies the problem of a line inclusion in a medium possessing coupled piezoelectric, piezomagnetic and magnetoelectric effects. Based on the extended Stroh formalism, ... [more]

This paper studies the problem of a line inclusion in a medium possessing coupled piezoelectric, piezomagnetic and magnetoelectric effects. Based on the extended Stroh formalism, the general two-dimensional solutions to the magnetoelectroelastic problem are obtained, involving five analytic functions of different variables. The magnetic, electric and elastic fields around the inclusion are given. Expressions of the stresses, electric field and magnetic field in the vicinity of the inclusion tip are derived and the field intensity factors are provided. The energy release rate is written in terms of those field intensity factors. Solutions for some special cases, including the electrically and/or magnetically insulated/conductive inclusions/cracks, are also established. Explicit algebraic results are given for a special case of an anti-plane crack in a magnetoelectroelastic medium. © 2010 - IOS Press and the authors.

DOI 10.3233/JAE-2010-1305
Citations Scopus - 1
2010 Sims AM, Stait-Gardner T, Fong L, Morley JW, Price WS, Hoffman M, et al., 'Elastic and viscoelastic properties of porcine subdermal fat using MRI and inverse FEA', Biomechanics and Modeling in Mechanobiology, 9 703-711 (2010)

There is a scarcity of investigation into the mechanical properties of subdermal fat. Recently, progress has been made in the determination of subdermal stress and strain distribu... [more]

There is a scarcity of investigation into the mechanical properties of subdermal fat. Recently, progress has been made in the determination of subdermal stress and strain distributions. This requires accurate constitutive modelling and consideration of the subdermal tissues. This paper reports the results of a study to estimate non-linear elastic and viscoelastic properties of porcine subdermal fat using a simple constitutive model. High-resolution magnetic resonance imaging (MRI) was used to acquire a time series of coincident images during a confined indentation experiment. Inverse finite element analysis was used to estimate the material parameters. The Neo Hookean model was used to represent the elastic behaviour (µ = 0.53 ± 0.31 kPa), while a single-element Prony series was used to model the viscoelastic response (a = 0.39 ± 0.03, t = 700 ± 255 s). © 2010 Springer-Verlag.

DOI 10.1007/s10237-010-0207-9
Citations Scopus - 18Web of Science - 17
2010 Arsecularatne JA, Hoffman M, 'On the wear mechanism of human dental enamel', Journal of the Mechanical Behavior of Biomedical Materials, 3 347-356 (2010)

The mechanisms and controlling factors in human enamel wear are not fully understood yet. To address this problem, we have used focused ion beam (FIB) milling and field emission s... [more]

The mechanisms and controlling factors in human enamel wear are not fully understood yet. To address this problem, we have used focused ion beam (FIB) milling and field emission scanning electron microscopy (FESEM) to investigate the processes taking place below the wear surface of enamel specimens from in vitro wear tests. These reveal the generation of subsurface cracks during wear of enamel. An analysis of published qualitative and quantitative experimental wear results for enamel as well as for ceramics shows the similarities of the wear processes taking place under similar contact conditions, despite the differences that exist between these two materials. It is shown that, for the considered conditions, fracture under elastic contact is responsible for enamel wear. © 2010 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.jmbbm.2010.01.006
Citations Scopus - 26Web of Science - 22
2009 Xie Z, Swain M, Hoffman MJ, 'Structural Integrity of Enamel: Experimental and Modeling (vol 88, pg 529, 2009)', JOURNAL OF DENTAL RESEARCH, 88 1059-1059 (2009)
DOI 10.1177/0022034509352599
2009 Borrero-López O, Vodenitcharova T, Hoffman M, Leo AJ, 'Fracture strength of polycrystalline silicon wafers for the photovoltaic industry', Journal of the American Ceramic Society, 92 2713-2717 (2009)

The fracture strength of polycrystalline silicon wafers has been investigated by means of twist and four-point bending tests. Under a twisting configuration, which generates high ... [more]

The fracture strength of polycrystalline silicon wafers has been investigated by means of twist and four-point bending tests. Under a twisting configuration, which generates high tensile stresses within the middle of the wafers, a unimodal distribution in strength is obtained. The characteristic strength and Weibull modulus are 131.0 MPa, and 14.4, respectively. Under a four-point bending configuration, which generates high stresses both at the surface and at the edges, an additive bimodal distribution is obtained. The first mode of the distribution has a characteristic strength of 76.0 MPa and a Weibull modulus of 1.6; the second mode has a characteristic strength of 161.2 MPa and a Weibull modulus of 11.5. Fractographic observations confirm that the first mode (lower strength) corresponds to wafers which failed from large edge chips (sizes up to 90 µm). Weibull analysis suggests that the second mode (higher strength) corresponds to wafers which failed from smaller surface chips (sizes up to 50 µm). The results obtained point to large edge chips as the most dangerous defects degrading the fracture strength of the wafers. This is of great relevance for the photovoltaic industry, as fracture of silicon wafers limits both the performance and lifetime of the solar cells, and production yields. © 2009 The American Ceramic Society.

DOI 10.1111/j.1551-2916.2009.03287.x
Citations Scopus - 17Web of Science - 17
2009 Matsutani A, Luo Z, Pojprapai S, Hoffman M, Pezzotti G, 'Visualization of highly graded oxygen vacancy profiles in lead-zirconate-titanate by spectrally resolved cathodoluminescence spectroscopy', Applied Physics Letters, 95 (2009)

The ultraviolet and visible cathodoluminescence (CL) emitted at room temperature from bulk hard lead-zirconate-titanate polycrystalline perovskite has been systematically collecte... [more]

The ultraviolet and visible cathodoluminescence (CL) emitted at room temperature from bulk hard lead-zirconate-titanate polycrystalline perovskite has been systematically collected before and after an annealing cycle conducted in a reducing atmosphere. Spectroscopic assessments have been made of the in-depth stoichiometric profile developed upon annealing from the sample surface toward the subsurface. Trapping of electronic charge and local atomic scale distortions in the perovskite oxygen octahedron influences the variation observed in visible CL emission, while lattice distortions upon annealing directly arise from the formation of oxygen vacancies. © 2009 American Institute of Physics.

DOI 10.1063/1.3245317
Citations Scopus - 2Web of Science - 1
2009 Xie ZH, Swain MV, Swadener G, Munroe P, Hoffman M, 'Effect of microstructure upon elastic behaviour of human tooth enamel', Journal of Biomechanics, 42 1075-1080 (2009)

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause ... [more]

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral-protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle. © 2009 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.jbiomech.2009.02.004
Citations Scopus - 43Web of Science - 43
2009 Xie Z, Swain MV, Hoffman MJ, 'Structural integrity of enamel: experimental and/modeling', Journal of Dental Research, 88 529-533 (2009)

Tooth enamel is the hardest tissue in the human body and is directly responsible for dental function. Due to its non-regenerative nature, enamel is unable to heal and repair itsel... [more]

Tooth enamel is the hardest tissue in the human body and is directly responsible for dental function. Due to its non-regenerative nature, enamel is unable to heal and repair itself biologically after damage. We hypothesized that with its unique microstructure, enamel possesses excellent resistance to contact- induced damage, regardless of loading direction. By combining instrumented indentation tests with microstructural analysis, we report that enamel can absorb indentation energy through shear deformation within its protein layers between apatite crystallites. Moreover, a near-isotropic inelastic response was observed when we analyzed indentation data in directions either perpendicular or parallel to the path of enamel prisms. An "effective" crystal orientation angle, 33°-34°, was derived for enamel micro- structure, independent of the loading direction. These findings will help guide the design of the nanostructural architecture of dental restorative materials.

DOI 10.1177/0022034509337130
Citations Scopus - 32Web of Science - 29
2009 Kemal I, Whittle A, Burford R, Vodenitcharova T, Hoffman M, 'Toughening of unmodified polyvinylchloride through the addition of nanoparticulate calcium carbonate', Polymer, 50 4066-4079 (2009)

PVC/CaCO3 polymer nanocomposites of differing compositions were produced using a two-roll mill and compression molding. The morphology was observed using transmission electron mic... [more]

PVC/CaCO3 polymer nanocomposites of differing compositions were produced using a two-roll mill and compression molding. The morphology was observed using transmission electron microscopy, and the static and dynamic mechanical and fracture properties determined. The presence of nanometer-sized CaCO3 particles led to a slight decrease in the tensile strength but improved the impact energy, the storage modulus and the fracture toughness. Fracture surface examination by scanning electron microscopy indicated that the enhanced fracture properties in the nanocomposites were caused by the assisted void formation at the particles. This hypothesis is supported by a microstructure-based finite element modeling based upon elastic-plastic deformation around a weakly bonded particle. Hence, this provides an explanation of both the uniaxial tensile behavior and enhanced toughness of the nanocomposites. © 2009 Elsevier Ltd.

DOI 10.1016/j.polymer.2009.06.028
Citations Scopus - 51Web of Science - 49
2009 Samat N, Burford R, Whittle A, Hoffman M, 'The effects of frequency on fatigue threshold and crack propagation rate in modified and unmodified polyvinyl chloride', Polymer Engineering and Science, 49 1299-1310 (2009)

The cyclic fatigue crack behavior of polyvinyl chloride (PVC), with (PVC-M) and without (PVC-U) chlorinated polyethylene (CPE) impact modifier, was studied. The effect of impact m... [more]

The cyclic fatigue crack behavior of polyvinyl chloride (PVC), with (PVC-M) and without (PVC-U) chlorinated polyethylene (CPE) impact modifier, was studied. The effect of impact modifier upon fatigue crack growth rate and threshold was evaluated at frequencies of 1, 7, and 20 Hz. It was shown that the addition of CPE lowered the threshold stress intensity factor amplitude for crack growth (¿Kth) of PVC-M compared to that of PVC-U at lower frequencies, and that the effect became more pronounced at lower frequency. At lower stress intensity factor amplitudes (below ¿K = 1 MPa·m 1/2), there was a slight difference between the crack growth rates of U- and M-PVC. The crack advance mechanism is investigated by microscopic observation of the crack tip process zone. Although the zone is relatively large in PVC-M, associated with higher toughness, it did not improve the fatigue crack growth resistance significantly. Fracture surface observations reveal a higher density of fibrils on the fatigued surface of PVC-M with the density, relative to that observed in PVC-U, reducing with frequency. It is therefore hypothesized that accelerated fibril failure is a mechanism of fatigue. © 2009 Society of Plastics Engineers.

DOI 10.1002/pen.21369
Citations Scopus - 6Web of Science - 6
2009 Dayal P, Savvides N, Hoffman M, 'Characterisation of nanolayered aluminium/palladium thin films using nanoindentation', Thin Solid Films, 517 3698-3703 (2009)

Structure, hardness, and elastic modulus of nanolayered aluminium/palladium thin films, with individual layer thickness varying from 1¿nm to 40¿nm, were investigated using transmi... [more]

Structure, hardness, and elastic modulus of nanolayered aluminium/palladium thin films, with individual layer thickness varying from 1¿nm to 40¿nm, were investigated using transmission electron microscopy (TEM) and nanoindentation. TEM micrographs indicated a sharp but not flat Al-Pd interface. With just 6.5% (v/v) Pd a hardness enhancement of ~ 200% was observed for nanolayered Al/Pd compared to the hardness of pure Al film. A maximum hardness enhancement of up to 350% was observed for nanolayered Al/Pd samples compared to the hardness of pure Al film when bilayer thickness was 2¿nm and Pd was 50% (v/v). Modulus enhancement was also observed for the nanolayered thin films. © 2009 Elsevier B.V. All rights reserved.

DOI 10.1016/j.tsf.2009.01.174
Citations Scopus - 21Web of Science - 19
2009 Dumklang M, Pattawong N, Punyodom W, Meepowpan P, Molloy R, Hoffman M, 'Novel tin(II) butoxides for use as initiators in the ring-opening polymerisation of e-caprolactone', Chiang Mai Journal of Science, 36 136-148 (2009)

Three tin(II) butoxides, namely: tin(II) n-butoxide, Sn(n-OBu)2; tin(II) i-butoxide, Sn(i-OBu)2; and tin(II) t-butoxide, Sn(t-OBu)2 were synthesized for use as coordination-insert... [more]

Three tin(II) butoxides, namely: tin(II) n-butoxide, Sn(n-OBu)2; tin(II) i-butoxide, Sn(i-OBu)2; and tin(II) t-butoxide, Sn(t-OBu)2 were synthesized for use as coordination-insertion initiators in the bulk ring-opening polymerisation of e-caprolactone (CL) at 120 °C. Two different methods of synthesis were compared: an old well-established method which gave solid products and a new modified method which, in the case of Sn(n-OBu)2, gave a novel liquid product. The liquid Sn(n-OBu)2 had the advantage for initiation purposes of being much more soluble than the solid Sn(n-OBu)2 due to its lower degree of molecular aggregation, a common characteristic of tin(II) alkoxides which limits their usefulness. Kinetic studies of CL polymerisation by dilatometry showed that the liquid Sn(n-OBu)2 initiator gave a much faster reaction with a higher first-order rate constant (kp = 8.25 l mol-1 min-1) than the solid Sn(n-OBu)2 initiator (kp = 2.96 l mol-1 min-1). The molecular weight of the polymer formed was also hi her. Increasing the bulkiness of the OBu group resulted in solid products with decreased solubility and initiating efficiency (for Sn(i-OBu)2, kp = 2.20 l mol-1 min-1; for Sn(t-OBu)2, kp = 0.69 l mol-1 min-1). It is concluded that the new modified method of initiator synthesis is capable of producing soluble tin(II) alkoxides which have the potential to offer improved kinetic and molecular weight control in the ring-opening polymerisation of cyclic esters.

Citations Scopus - 10Web of Science - 9
2009 Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'Contact damage of tetrahedral amorphous carbon thin films on silicon substrates', Journal of Materials Research, 24 3286-3293 (2009)

We have investigated the fracture behavior of tetrahedral amorphous carbon films, with thicknesses 0.15 (ultrathin), 0.5 (thin), and 1.2 (thick) microns on silicon substrates. To ... [more]

We have investigated the fracture behavior of tetrahedral amorphous carbon films, with thicknesses 0.15 (ultrathin), 0.5 (thin), and 1.2 (thick) microns on silicon substrates. To that end, the systems were progressively loaded using a nanoindenter with a spherical tip, and surface and cross sections were subsequently examined using a focused ion beam miller at different loads. A transition was found as a function of film thickness: for ultrathin and thin films, cracking (radial and lateral) initiated in the silicon substrate and followed a similar path in the films. Thicker films, on the other hand, provided a higher level of protection to the substrate, and cracking (lateral and radial at the interface) was constrained to the film. The damage modes and the transition obtained differ from those that occur in thick coatings. Lateral cracks are highly dangerous, leading to delamination of thick films and to spallation when thinner films are used. The results have implications concerning the mechanical reliability of microelectromechanical systems. © 2009 Materials Research Society.

DOI 10.1557/jmr.2009.0405
Citations Scopus - 3Web of Science - 3
2009 Idris MI, Vodenitcharova T, Hoffman M, 'Mechanical behaviour and energy absorption of closed-cell aluminium foam panels in uniaxial compression', Materials Science and Engineering A, 517 37-45 (2009)

Thin and thick panels of two types of aluminium closed-cell foams of ~0.20-0.31 g/cm3 (ALPORAS) and ~0.32-0.57 g/cm3 (ALULIGHT) density were tested in uniaxial compression and the... [more]

Thin and thick panels of two types of aluminium closed-cell foams of ~0.20-0.31 g/cm3 (ALPORAS) and ~0.32-0.57 g/cm3 (ALULIGHT) density were tested in uniaxial compression and the mechanical properties of the panels, plastic collapse strength, plateau stress and absorbed energy, were extracted. Their dependence on the foam density and specimen thickness was also ascertained. Micro-indentation tests were used to estimate the yield stresses of the parent materials. It was found that the higher density panels of ALULIGHT were also more anisotropic than the lower density panels of ALPORAS, and the collapse strength and the absorbed energy of both foams increased with density. More significant scatter the results was observed in the thin and higher density panels. © 2009 Elsevier B.V. All rights reserved.

DOI 10.1016/j.msea.2009.03.067
Citations Scopus - 71Web of Science - 63
2009 Allen B, Crosky A, Mcalpine I, Hoffman M, Munroe P, 'A blended approach to collaborative learning: Making large group teaching more student-centred', International Journal of Engineering Education, 25 569-576 (2009)

Current educational thinking promotes a student-centred approach to teaching as more engaging and challenging for students, leading to improved learning outcomes. But what is &apo... [more]

Current educational thinking promotes a student-centred approach to teaching as more engaging and challenging for students, leading to improved learning outcomes. But what is 'student-centred' learning, and how can it be achieved in a higher education setting with very large classes and content-rich courses? In a materials engineering course for 300 first-year engineers, an online group project was introduced to add authenticity and collaborative activity into the course, and to improve student engagement. We explore the design, development and implementation of the project, and see if the intended outcomes were achieved. © 2009 TEMPUS Publications.

Citations Scopus - 5Web of Science - 5
2009 Yu A, Genenko J, Glaum O, Hirsch H, Kungl H, Hoffman M, Granzow T, 'Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries', PHYSICAL REVIEW B, 80 (2009)
DOI 10.1103/PhysRevB.80.224109
2009 Pojprapai S, Russell J, Man H, Jones JL, Daniels JE, Hoffman M, 'Frequency effects on fatigue crack growth and crack tip domain-switching behavior in a lead zirconate titanate ceramic', ACTA MATERIALIA, 57 3932-3940 (2009)
DOI 10.1016/j.actamat.2009.04.054
Citations Scopus - 30Web of Science - 30
2009 Borrero-López O, Hoffman M, Bendavid A, Martin PJ, 'Reverse size effect in the fracture strength of brittle thin films', Scripta Materialia, 60 937-940 (2009)

The Weibull size effect, consisting of an increase in fracture strength with decreasing specimen size, constitutes the basis of the probabilistic design of brittle structures. Her... [more]

The Weibull size effect, consisting of an increase in fracture strength with decreasing specimen size, constitutes the basis of the probabilistic design of brittle structures. Here we present evidence of a reverse size effect in submicron amorphous carbon films. Underlying this effect is the presence of critical defects of comparable size in all films. This leads to higher stress intensity factors, and concomitant decrease in strength, with decreasing thickness. The results have implications concerning the mechanical reliability of submicron scale devices. © 2009 Acta Materialia Inc.

DOI 10.1016/j.scriptamat.2009.01.042
Citations Scopus - 11Web of Science - 12
2009 Moon RJ, Hoffman M, Roedel J, Tochino S, Pezzotti G, 'Evaluation of crack-tip stress fields on microstructural-scale fracture in Al-Al2O3 interpenetrating network composites', ACTA MATERIALIA, 57 570-581 (2009)
DOI 10.1016/j.actamat.2008.09.043
Citations Scopus - 10Web of Science - 8
2008 Xie Z, Swain M, Munroe P, Hoffman M, 'On the critical parameters that regulate the deformation behaviour of tooth enamel', BIOMATERIALS, 29 2697-2703 (2008)
DOI 10.1016/j.biomaterials.2008.02.022
Citations Scopus - 48Web of Science - 47
2008 Singh RK, Tilbrook MT, Xie ZH, Bendavid A, Martin PJ, Munroe P, Hoffman M, 'Contact damage evolution in diamondlike carbon coatings on ductile substrates', JOURNAL OF MATERIALS RESEARCH, 23 27-36 (2008)
DOI 10.1557/JMR.2008.0030
Citations Scopus - 28Web of Science - 24
2008 Singh RK, Munroe P, Hoffman M, 'Effect of temperature on metastable phases induced in silicon during nanoindentation', JOURNAL OF MATERIALS RESEARCH, 23 245-249 (2008)
DOI 10.1557/JMR.2008.0023
Citations Scopus - 10Web of Science - 10
2008 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Berkovich indentation of diamondlike carbon coatings on silicon substrates', JOURNAL OF MATERIALS RESEARCH, 23 1862-1869 (2008)
DOI 10.1557/JMR.2008.0232
Citations Scopus - 13Web of Science - 13
2008 Singh RK, Xie ZH, Bendavid A, Martin PJ, Munroe P, Hoffman H, 'Effect of substrate roughness on the contact damage of DLC coatings', DIAMOND AND RELATED MATERIALS, 17 975-979 (2008)
DOI 10.1016/j.diamond.2008.02.037
Citations Scopus - 26Web of Science - 24
2008 Man H, Furukawa T, Hoffman M, Imlao S, 'An indirect implicit technique for modelling piezoelectric ceramics', COMPUTATIONAL MATERIALS SCIENCE, 43 629-640 (2008)
DOI 10.1016/j.commatsci.2008.01.008
Citations Scopus - 8Web of Science - 7
2008 Xie Z, Kilpatrick NM, Swain MV, Munroe PR, Hoffman M, 'Transmission electron microscope characterisation of molar-incisor-hypomineralisation', JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 19 3187-3192 (2008)
DOI 10.1007/s10856-008-3441-2
Citations Scopus - 34Web of Science - 35
2008 Xie ZH, Hoffman M, Munroe P, Bendavid A, Martin PJ, 'Deformation mechanisms of TiN multilayer coatings alternated by ductile or stiff interlayers', ACTA MATERIALIA, 56 852-861 (2008)
DOI 10.1016/j.actamat.2007.10.047
Citations Scopus - 68Web of Science - 58
2008 Imlao SP, Jones JL, Studer AJ, Russell J, Valanoor N, Hoffman M, 'Ferroelastic domain switching fatigue in lead zirconate titanate ceramics', ACTA MATERIALIA, 56 1577-1587 (2008)
DOI 10.1016/j.actamat.2007.11.044
Citations Scopus - 23Web of Science - 22
2008 Borrero-Lopez O, Hoffman M, Bendavid A, Martin PJ, 'A simple nanoindentation-based methodology to assess the strength of brittle thin films', ACTA MATERIALIA, 56 1633-1641 (2008)
DOI 10.1016/j.actamat.2007.12.007
Citations Scopus - 20Web of Science - 16
2008 Quadir MZ, Woiz A, Hoffman M, Ferry M, 'Influence of processing parameters on the bond toughness of roll-bonded aluminium strip', SCRIPTA MATERIALIA, 58 959-962 (2008)
DOI 10.1016/j.scriptamat.2008.01.022
Citations Scopus - 61Web of Science - 52
2007 Eichler J, Roedel J, Eisele U, Hoffman M, 'Effect of grain size on mechanical properties of submicrometer 3Y-TZP: Fracture strength and hydrothermal degradation', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 90 2830-2836 (2007)
DOI 10.1111/j.1551-2916.2007.01643.x
Citations Scopus - 68Web of Science - 61
2007 Hoffman M, Hu XZ, Ye L, 'Fracture of materials: Moving forwards - Yiu-Wing Mai', ENGINEERING FRACTURE MECHANICS, 74 1007-1008 (2007)
DOI 10.1016/j.engfracmech.2006.12.019
2007 Tilbrook M, Hoffman M, 'Approximation of curved cracks under mixed-mode loading', ENGINEERING FRACTURE MECHANICS, 74 1026-1040 (2007)
DOI 10.1016/j.engfracmech.2006.12.008
Citations Scopus - 8Web of Science - 4
2007 Daniels JE, Finlayson TR, Davis M, Damjanovic D, Studer AJ, Hoffman M, Jones JL, 'Neutron diffraction study of the polarization reversal mechanism in [111](c)-oriented Pb(Zn1/3Nb2/3)O-3-xPbTiO(3)', JOURNAL OF APPLIED PHYSICS, 101 (2007)
DOI 10.1063/1.2733636
Citations Scopus - 32Web of Science - 32
2007 Ma LW, Cairney JM, McGrouther D, Hoffman M, Munroe PR, 'Three dimensional imaging of deformation modes in TiN-based thin film coatings', THIN SOLID FILMS, 515 3190-3195 (2007)
DOI 10.1016/j.tsf.2006.01.034
Citations Scopus - 26Web of Science - 25
2007 Xie Z-H, Singh R, Bendavid A, Martin PJ, Munroe PR, Hoffman M, 'Contact damage evolution in a diamond-like carbon (DLC) coating on a stainless steel substrate', THIN SOLID FILMS, 515 3196-3201 (2007)
DOI 10.1016/j.tsf.2006.01.035
Citations Scopus - 66Web of Science - 63
2007 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Deformation behaviour of DLC coatings on (111) silicon substrates', THIN SOLID FILMS, 516 267-271 (2007)
DOI 10.1016/j.tsf.2007.06.032
Citations Scopus - 16Web of Science - 16
2007 Tilbrook MT, Rutgers L, Moon RJ, Hoffman M, 'Fatigue crack propagation resistance in homogeneous and graded alumina-epoxy composites', INTERNATIONAL JOURNAL OF FATIGUE, 29 158-167 (2007)
DOI 10.1016/j.ijfatigue.2006.01.015
Citations Scopus - 11Web of Science - 10
2007 Jones JL, Hoffman M, Vogel SC, 'Ferroelastic domain switching in lead zirconate titanate measured by in situ neutron diffraction', MECHANICS OF MATERIALS, 39 283-290 (2007)
DOI 10.1016/j.mechmat.2006.06.005
Citations Scopus - 44Web of Science - 42
2007 Ye L, Hu X, Hoffman M, 'Professor Yiu-Wing Mai', COMPOSITES SCIENCE AND TECHNOLOGY, 67 149-150 (2007)
DOI 10.1016/j.compscitech.2006.07.013
2007 Xie ZH, Hoffman M, Munroe P, Singh R, Bendavid A, Martin PJ, 'Microstructural response of TiN monolithic and multilayer coatings during microscratch testing', JOURNAL OF MATERIALS RESEARCH, 22 2312-2318 (2007)
DOI 10.1557/JMR.2007.0292
Citations Scopus - 40Web of Science - 37
2007 Heilmann F, Standard OC, Mueller FA, Hoffman M, 'Development of graded hydroxyapatite/CaCO3 composite structures for bone ingrowth', JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 18 1817-1824 (2007)
DOI 10.1007/s10856-007-3028-3
Citations Scopus - 27Web of Science - 22
2007 Tilbrook MT, Paton DJ, Xie Z, Hoffman M, 'Microstructural effects on indentation failure mechanisms in TiN coatings: Finite element simulations', ACTA MATERIALIA, 55 2489-2501 (2007)
DOI 10.1016/j.actamat.2006.11.043
Citations Scopus - 61Web of Science - 57
2007 Jones JL, Motahari SM, VarlioglU M, Lienert U, Bernier JV, Hoffman M, Uestuendag E, 'Crack tip process zone domain switching in a soft lead zirconate titanate ceramic', ACTA MATERIALIA, 55 5538-5548 (2007)
DOI 10.1016/j.actamat.2007.06.012
Citations Scopus - 51Web of Science - 46
2007 Xie Z-H, Mahoney EK, Kilpatrick NM, Swain MV, Hoffman M, 'On the structure-property relationship of sound and hypomineralized enamel', ACTA BIOMATERIALIA, 3 865-872 (2007)
DOI 10.1016/j.actbio.2007.05.007
Citations Scopus - 59Web of Science - 54
2007 Hoffman M, Deneke C, Kidson L, 'Effect of crack growth resistance upon fracture of ceramic/polymer graded interfaces', Journal of the Australian Ceramic Society, 43 18-23 (2007)

A crack initiated perpendicular to a stiffness gradient deflects as it propagates due to inherent mode mixity. A model experiment, finite element modelling and an analytical model... [more]

A crack initiated perpendicular to a stiffness gradient deflects as it propagates due to inherent mode mixity. A model experiment, finite element modelling and an analytical model are used to shown that when crack bridging occurs that the extent of crack deflection may be reduced.

2007 Man H, Furukawa T, Hoffman M, Imlao S, Lou ZH, 'An indirect implicit model for frequency dependent hystereses of piezoelectric ceramics', Journal of the Australian Ceramic Society, 43 169-174 (2007)

The hysteretic behaviour of piezoelectric ceramics is not only dependent on the level of applied loading but also on frequency. In order to improve the performance of piezoelectri... [more]

The hysteretic behaviour of piezoelectric ceramics is not only dependent on the level of applied loading but also on frequency. In order to improve the performance of piezoelectric components, this paper presents an indirect implicit model for the hystereses of piezoelectric ceramics while considering the effect on various loading frequency of applied electrical field. The proposed model is able to reproduce the hysteretic response under these conditions. Experimental data of a type of piezoelectric ceramic, lead zirconate titanate (PZT), was used in the numerical examples to demonstrate the performance of the proposed model. Neural networks are used as the implicit modelling technique due to the capability of nonparametric mapping of the experimental data as well as the feature of interpolation. Results of the numerical examples show that the proposed model is able to simulate the desired frequency dependent hysteretic behaviour while providing good correlation with the experimental data.

Citations Scopus - 2
2006 Pojprapai (Imlao) S, Jones JL, Hoffman M, 'Domain switching under cyclic mechanical loading in lead zirconate titanate', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 89 3567-3569 (2006)
DOI 10.1111/j.1551-2916.2006.01260.x
Citations Scopus - 17Web of Science - 14
2006 Jones JL, Hoffman M, 'R-curve and stress-strain behavior of ferroelastic ceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 89 3721-3727 (2006)
DOI 10.1111/j.1551-2916.2006.01300.x
Citations Scopus - 31Web of Science - 31
2006 Pojprapai S, Jones JL, Hoffman M, 'Determination of domain orientation in lead zirconate titanate ceramics by Raman spectroscopy', APPLIED PHYSICS LETTERS, 88 (2006)
DOI 10.1063/1.2195772
Citations Scopus - 21Web of Science - 19
2006 Jones JL, Hoffman M, Daniels JE, Studer AJ, 'Direct measurement of the domain switching contribution to the dynamic piezoelectric response in ferroelectric ceramics', APPLIED PHYSICS LETTERS, 89 (2006)
DOI 10.1063/1.2338756
Citations Scopus - 119Web of Science - 119
2006 Moon RJ, Hoffman M, Tochino S, Lee CJ, Pezzotti G, 'Fluorescence spectroscopy analysis of Al-Al2O3 composites with coarse interpenetrating networks', JOURNAL OF MATERIALS SCIENCE, 41 7571-7579 (2006)
DOI 10.1007/s10853-006-0843-8
Citations Scopus - 1Web of Science - 1
2006 Haq AJ, Munroe PR, Hoffman M, Martin PJ, Bendavid A, 'Nanoindentation-induced deformation behaviour of diamond-like carbon coatings on silicon substrates', THIN SOLID FILMS, 515 1000-1004 (2006)
DOI 10.1016/j.tsf.2006.07.074
Citations Scopus - 20Web of Science - 19
2006 Xie ZH, Hoffman M, Moon RJ, Munroe PR, Cheng YB, 'Sliding wear of calcium alpha-sialon ceramics', WEAR, 260 387-400 (2006)
DOI 10.1016/j.wear.2005.02.065
Citations Scopus - 14Web of Science - 12
2006 Xie Z-H, Hoffman M, Moon RJ, Munroe PR, Cheng Y-B, 'Sliding wear behaviour of Ca alpha-sialon ceramics at 600 degrees C in air', WEAR, 260 1356-1360 (2006)
DOI 10.1016/j.wear.2005.09.011
Citations Scopus - 14Web of Science - 14
2006 Ma LW, Cairney JM, Hoffman MJ, Munroe PR, 'Deformation and fracture of TiN and TiAlN coatings on a steel substrate during nanoindentation', SURFACE & COATINGS TECHNOLOGY, 200 3518-3526 (2006)
DOI 10.1016/j.surfcoat.2004.09.034
Citations Scopus - 40Web of Science - 35
2006 Winkelmann A, Cairney JM, Hoffman MJ, Martin PJ, Bendavid A, 'Zr-Si-N films fabricated using hybrid cathodic arc and chemical vapour deposition: Structure vs. properties', SURFACE & COATINGS TECHNOLOGY, 200 4213-4219 (2006)
DOI 10.1016/j.surfcoat.2005.01.004
Citations Scopus - 32Web of Science - 34
2006 Bendavid A, Martin PJ, Preston EW, Cairney J, Xie ZH, Hoffman M, 'Deposition of nanocomposite thin films by a hybrid cathodic arc and chemical vapour technique', SURFACE & COATINGS TECHNOLOGY, 201 4139-4144 (2006)
DOI 10.1016/j.surfcoat.2006.08.021
Citations Scopus - 29Web of Science - 25
2006 Xie ZH, Hoffman M, Moon RJ, Munroe PR, 'Deformation of a hard coating on ductile substrate system during nanoindentation: Role of the coating microstructure', JOURNAL OF MATERIALS RESEARCH, 21 437-447 (2006)
DOI 10.1557/JMR.2006.0050
Citations Scopus - 25Web of Science - 26
2006 Xie Z-H, Munroe PR, McGrouther D, Singh RK, Hoffman M, Bendavid A, et al., 'Three-dimensional study of indentation-induced cracks in an amorphous carbon coating on a steel substrate', JOURNAL OF MATERIALS RESEARCH, 21 2600-2605 (2006)
DOI 10.1557/JMR.2006.0313
Citations Scopus - 13Web of Science - 13
2006 Jones JL, Hoffman M, Daniels JE, Studer AJ, 'Ferroelastic contribution to the piezoelectric response in lead zirconate titanate by in situ stroboscopic neutron diffraction', PHYSICA B-CONDENSED MATTER, 385 100-102 (2006)
DOI 10.1016/j.physb.2006.05.115
Citations Scopus - 4Web of Science - 3
2006 Jones JL, Hoffman M, Vogel SC, 'Orientation-dependent lattice strains in lead zirconate titanate under mechanical compression by in situ neutron diffraction', PHYSICA B-CONDENSED MATTER, 385 548-551 (2006)
DOI 10.1016/j.physb.2006.05.288
Citations Scopus - 10Web of Science - 10
2006 Jayaram V, Bhowmick S, Xie ZH, Math S, Hoffman M, Biswas SK, 'Contact deformation of TiN coatings on metallic substrates', MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 423 8-13 (2006)
DOI 10.1016/j.msea.2005.09.123
Citations Scopus - 33Web of Science - 30
2006 Eichler J, Hoffman M, Eisele U, Roedel J, 'R-curve behaviour of 2Y-TZP with submicron grain size', JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 26 3575-3582 (2006)
DOI 10.1016/j.jeurceramsoc.2005.11.012
Citations Scopus - 20Web of Science - 21
2006 Moon RJ, Hoffman M, Bowman K, Trumble K, 'Layer orientation effects on the R-curve behavior of multilayered alumina-zirconia composites', COMPOSITES PART B-ENGINEERING, 37 449-458 (2006)
DOI 10.1016/j.compositesb.2006.02.021
Citations Scopus - 7Web of Science - 6
2006 Chaiwan S, Hoffman M, Munroe P, 'Investigation of sliding wear surfaces in alumina using transmission electron microscopy', SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 7 826-833 (2006)
DOI 10.1016/j.stam.2006.11.007
Citations Scopus - 12Web of Science - 9
2006 Tilbrook MT, Rozenburg K, Steffler ED, Rutgers L, Hoffman M, 'Crack propagation paths in layered, graded composites', COMPOSITES PART B-ENGINEERING, 37 490-498 (2006)
DOI 10.1016/j.compositesb.2006.02.012
Citations Scopus - 35Web of Science - 22
2005 Moon RJ, Tilbrook M, Hoffman M, Neubrand A, 'Al-Al2O3 composites with interpenetrating network structures: Composite modulus estimation', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 88 666-674 (2005)
DOI 10.1111/j.1551-2916.2005.00115.x
Citations Scopus - 37Web of Science - 34
2005 Jones JL, Salz CRJ, Hoffman M, 'Ferroelastic fatigue of a soft PZT ceramic', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 88 2788-2792 (2005)
DOI 10.1111/j.1551-2916.2005.00520.x
Citations Scopus - 21Web of Science - 17
2005 Tilbrook MT, Hoffman M, Reimanis IE, 'Finite-element simulations of cracks near interfaces: Effects of thermal, elastic, and plastic mismatch', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 88 2833-2838 (2005)
DOI 10.1111/j.1551-2916.2005.00545.x
Citations Scopus - 4Web of Science - 3
2005 Tilbrook MT, Moon RJ, Hoffman M, 'Finite element simulations of crack propagation in functionally graded materials under flexural loading', ENGINEERING FRACTURE MECHANICS, 72 2444-2467 (2005)
DOI 10.1016/j.engfracmech.2005.04.001
Citations Scopus - 35Web of Science - 24
2005 Jones JL, Hoffman M, Bowman KJ, 'Saturated domain switching textures and strains in ferroelastic ceramics', JOURNAL OF APPLIED PHYSICS, 98 (2005)
DOI 10.1063/1.1988978
Citations Scopus - 97Web of Science - 89
2005 Cairney JM, Hoffman MJ, Munroe PR, Martin PJ, Bendavid A, 'Deformation and fracture of Ti-Si-N nanocomposite films', THIN SOLID FILMS, 479 193-200 (2005)
DOI 10.1016/j.tsf.2004.11.185
Citations Scopus - 34Web of Science - 31
2005 Ma LW, Cairney JM, Hoffman M, Munroe PR, 'Deformation mechanisms operating during nanoindentation of TiN coatings on steel substrates', SURFACE & COATINGS TECHNOLOGY, 192 11-18 (2005)
DOI 10.1016/j.surfcoat.2004.04.002
Citations Scopus - 49Web of Science - 50
2005 Cairney JM, Munroe PR, Hoffman M, 'The application of focused ion beam technology to the characterization of coatings', SURFACE & COATINGS TECHNOLOGY, 198 165-168 (2005)
DOI 10.1016/j.surfcoat.2004.10.042
Citations Scopus - 37Web of Science - 33
2005 Martin PJ, Bendavid A, Cairney JM, Hoffman M, 'Nanocomposite Ti-Si-N, Zr-Si-N, Ti-Al-Si-N, Ti-Al-V-Si-N thin film coatings deposited by vacuum arc deposition', SURFACE & COATINGS TECHNOLOGY, 200 2228-2235 (2005)
DOI 10.1016/j.surfcoat.2004.06.012
Citations Scopus - 94Web of Science - 89
2005 Tilbrook MT, Moon RJ, Hoffman M, 'Crack propagation in graded composites', COMPOSITES SCIENCE AND TECHNOLOGY, 65 201-220 (2005)
DOI 10.1016/j.compscitech.2004.07.004
Citations Scopus - 104Web of Science - 91
2005 Tilbrook MT, Moon R, Hoffman M, 'On the mechanical properties of alumina-epoxy composites with an interpenetrating network structure', MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 393 170-178 (2005)
DOI 10.1016/j.msea.2004.10.004
Citations Scopus - 50Web of Science - 41
2005 Bendavid A, Martin PJ, Cairney J, Hoffman M, Fischer-Cripps AC, 'Deposition of nanocomposite TiN-Si3N4 thin films by hybrid cathodic arc and chemical vapor process', APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 81 151-158 (2005)
DOI 10.1007/s00339-004-2951-0
Citations Scopus - 27Web of Science - 26
2005 Tilbrook MT, Reimanis IE, Rozenburg K, Hoffman M, 'Effects of plastic yielding on crack propagation near ductile/brittle interfaces', ACTA MATERIALIA, 53 3935-3949 (2005)
DOI 10.1016/j.actamat.2005.04.045
Citations Scopus - 23Web of Science - 16
2005 Bhowmick S, Bhide R, Hoffman M, Jayaram V, Biswas SK, 'Fracture mode transitions during indentation of columnar TiN coatings on metal', PHILOSOPHICAL MAGAZINE, 85 2927-2945 (2005)
DOI 10.1080/14786430500155213
Citations Scopus - 24Web of Science - 24
2005 Tilbrook MT, Moon RJ, Hoffman M, 'Curved crack propagation in homogeneous and graded materials', FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES, 28 939-950 (2005)
DOI 10.1111/j.1460-2695.2005.00927.x
Citations Scopus - 7Web of Science - 6
2005 Salz C, Hoffman M, Westram I, Rodel J, 'Cyclic Fatigue Crack Growth in PZT Under Mechanical Loading', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 1331-1333 (2005)
DOI 10.1111/j.1551-2916.2005.00235.x
Citations Web of Science - 23
2004 Xie ZH, Hoffman M, Moon RJ, Munroe PR, Cheng YB, 'Subsurface indentation damage and mechanical characterization of alpha-sialon ceramics', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 87 2114-2124 (2004)
Citations Scopus - 12Web of Science - 12
2004 Ma LW, Cairney JM, Hoffman MJ, Munroe PR, 'Characterization of TiN thin films subjected to nanoindentation using focused ion beam milling', APPLIED SURFACE SCIENCE, 237 631-635 (2004)
DOI 10.1016/j.apsusc.2004.06.135
Citations Web of Science - 15
2004 Bhowmick S, Xie ZH, Hoffman M, Jayaram V, Biswas SK, 'Nature of contact deformation of TiN films on steel', JOURNAL OF MATERIALS RESEARCH, 19 2616-2624 (2004)
DOI 10.1557/JMR.2004.0339
Citations Scopus - 34Web of Science - 34
2004 Furukawa T, Hoffman M, 'Accurate cyclic plastic analysis using a neural network material model', ENGINEERING ANALYSIS WITH BOUNDARY ELEMENTS, 28 195-204 (2004)
DOI 10.1016/S0955-7997(03)00050-X
Citations Scopus - 33Web of Science - 29
2004 Cairney JM, Tsukano R, Hoffman MJ, Yang M, 'Degradation of TiN coatings under cyclic loading', ACTA MATERIALIA, 52 3229-3237 (2004)
DOI 10.1016/j.actamat.2004.03.022
Citations Scopus - 53Web of Science - 54
2003 Xie ZH, Hoffman M, Moon RJ, Munroe P, Cheng YB, 'Scratch damage in ceramics: Role of microstructure', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 86 141-148 (2003)
DOI 10.1111/j.1151-2916.2003.tb03291.x
Citations Scopus - 16Web of Science - 13
2003 Xie ZH, Munroe PR, Moon RJ, Hoffman M, 'Characterization of surface contact-induced fracture in ceramics using a focused ion beam miller', WEAR, 255 651-656 (2003)
DOI 10.1016/S0043-1648(03)00043-7
Citations Scopus - 21Web of Science - 21
2003 Xie ZH, Moon RJ, Hoffman M, Munroe P, Cheng YB, 'Role of microstructure in the grinding and polishing of alpha-sialon ceramics', JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 23 2351-2360 (2003)
DOI 10.1016/S0955-2219(03)00046-3
Citations Scopus - 30Web of Science - 24
2003 Xie ZH, Munroe PR, Hoffman M, Moon RJ, Cheng YB, 'Application of focused ion beam miller in fracture characterization', ADVANCED CERAMICS AND COMPOSITES, 247 297-300 (2003)
DOI 10.4028/www.scientific.net/KEM.247.297
Citations Web of Science - 1
2002 Xie ZH, Hoffman M, Cheng YB, 'Microstructural tailoring and characterization of a calcium a-SiAlON composition', Journal of the American Ceramic Society, 85 812-818 (2002)

Three calcium a-SiAlON microstructures-namely, fine-grained, bimodal, and large elongated-were developed using powders of the same composition and then characterized. The evolutio... [more]

Three calcium a-SiAlON microstructures-namely, fine-grained, bimodal, and large elongated-were developed using powders of the same composition and then characterized. The evolution of grain size and morphology was determined to be a process of nucleation and growth that could be controlled with a two-step sintering technique. The extent of texture was identified in the as-hot-pressed materials as a function of sintering conditions. Samples with different microstructures exhibited different hardness and fracture toughness. The true hardness was derived from the intrinsic relation between applied loads and indent sizes. The effect of microstructure on hardness and fracture toughness was analyzed.

Citations Scopus - 32Web of Science - 29
2002 Moon RJ, Hoffman M, Hilden J, Bowman K, Trumble K, Rödel J, 'Weight function analysis on the R-curve behavior of multilayered alumina-zirconia composites', Journal of the American Ceramic Society, 85 1505-1511 (2002)

The single-edge V-notched-beam (SEVNB) testing geometry was used to measure the crack growth resistance (R-curve) behavior of multilayered alumina-zirconia composites. Fracture me... [more]

The single-edge V-notched-beam (SEVNB) testing geometry was used to measure the crack growth resistance (R-curve) behavior of multilayered alumina-zirconia composites. Fracture mechanics weight function analysis was applied to predict the R-curve behavior of multilayered composites having a stepwise change in composition. These results were then used to differentiate the influence of residual stresses from crack-bridging stresses on the measured R-curve behavior.

DOI 10.1111/j.1151-2916.2002.tb00304.x
Citations Scopus - 38Web of Science - 32
2002 Moon RJ, Hoffman M, Hilden J, Bowman KJ, Trumble KP, Rödel J, 'R-curve behavior in alumina-zirconia composites with repeating graded layers', Engineering Fracture Mechanics, 69 1647-1665 (2002)

The single-edge-V-notched-beam testing geometry was used to measure the crack growth resistance (R-curve) behavior of multilayer graded alumina-zirconia composites for crack exten... [more]

The single-edge-V-notched-beam testing geometry was used to measure the crack growth resistance (R-curve) behavior of multilayer graded alumina-zirconia composites for crack extensions parallel to the graded direction. Fracture mechanics weight function analysis was applied to explain the R-curve behavior of a compositional and grain-size graded microstructure. The results were then used to differentiate the influence of residual stress from other closure stresses, attributed to crack bridging, on the measured R-curve behavior. © 2002 Elsevier Science Ltd. All rights reserved.

DOI 10.1016/S0013-7944(02)00050-4
Citations Scopus - 39Web of Science - 29
2002 Chaiwan S, Hoffman M, Munroe P, Stiefel U, 'Investigation of sub-surface damage during sliding wear of alumina using focused ion-beam milling', Wear, 252 531-539 (2002)

In this work contact pressure and sliding distance-induced changes in wear rate and mechanism, and friction behaviour of alumina are investigated by consideration of sub-surface d... [more]

In this work contact pressure and sliding distance-induced changes in wear rate and mechanism, and friction behaviour of alumina are investigated by consideration of sub-surface damage. Sub-surface cracking and the formation of tribochemical reaction products are observed through the use of a novel sectioning technique; focused ion-beam milling. Initially wear rate experiments with three different grain sizes and different contact loads were undertaken. These were followed by extensive sub-surface microscopic investigations. Wear experiments, undertaken on a pin-on-disc tribometer over a range of contact pressures, revealed that wear mechanisms changed as contact pressure decreased. Both wear rate and friction were monitored. Debris and surface layers which formed were characterised using X-ray photoelectron spectroscopy (XPS). This identified an oxide/hydroxide layer which formed during wear and which was found to significantly affect friction. The nature of this layer varied significantly with contact pressure and sliding distance. It was found that mild wear of alumina in air involves the continual formation and removal of a surface layer at differing rates. © 2002 Elsevier Science B.V. All rights reserved.

DOI 10.1016/S0043-1648(01)00898-5
Citations Scopus - 22Web of Science - 19
2002 Furukawa T, Sugata T, Yoshimura S, Hoffman M, 'An automated system for simulation and parameter identification of inelastic constitutive models', Computer Methods in Applied Mechanics and Engineering, 191 2235-2260 (2002)

This paper presents an automated system for parameter identification of inelastic constitutive models. The system can find good approximate parameters for various identification p... [more]

This paper presents an automated system for parameter identification of inelastic constitutive models. The system can find good approximate parameters for various identification problems under a user-friendly environment. In order to identify parameters efficiently and in a robust manner, an optimisation method is first proposed. The paper then describes the generalisations applied of modelling, simulation and identification for its various identification uses. Finally, a system, which is developed in conjunction with the generalisations, is described. The performances of the proposed optimisation method and the developed system were investigated with actual material data, and their effectiveness was consequently confirmed. © 2002 Published by Elsevier Science B.V.

DOI 10.1016/S0045-7825(01)00375-9
Citations Scopus - 52Web of Science - 43
2002 Dai Y, Zhang Y, Nan C, Hoffman M, Huang M, Li J, 'Growth and microstructure of AIN whiskers and dendrites', Journal of University of Science and Technology Beijing: Mineral Metallurgy Materials (Eng Ed), 9 118-120 (2002)

AIN whiskers or dendrites were synthesized with a sublimation-recrystallization method by using Al, AIN powders and some additives as raw materials. Whiskers with different sizes ... [more]

AIN whiskers or dendrites were synthesized with a sublimation-recrystallization method by using Al, AIN powders and some additives as raw materials. Whiskers with different sizes that featured high purity and good crystallinity were obtained by controlling temperature and gas supersaturation in the reaction container. The whiskers were described as long and straight single crystals of approximately 1-30 µm in diameter by the centimeter range in length. However, AIN dendrites were about 1 mm in diameter by 0.5 cm in length, and showed an obviously preferential growth orientation, i.e., perpendicular to [2 1¯ 1¯ 1] and [1 0 1¯ 1] planes. It is concluded that the whiskers or dendrites grow via the vapor-solid mechanism.

Citations Scopus - 1
2001 Box VJ, Munroe PR, Crosky AC, Hoffman MJ, Krauklis P, Ford RAJ, 'Increasing Student Involvement in Materials Engineering Service Subjects for Mechanical Engineers', International Journal of Engineering Education, 17 529-537 (2001)

The design and preparation of a series of interactive computer-based tutorials for first year mechanical engineering students allowed them to become actively involved in their lea... [more]

The design and preparation of a series of interactive computer-based tutorials for first year mechanical engineering students allowed them to become actively involved in their learning as a means of overcoming the problems with large tutorial groups. The students were taking an introductory subject in materials engineering, and the tutorials led the students through a number of modules providing information, simulations and examples. The student response to these tutorials was overwhelmingly positive, although some negative responses suggested that some tutorials were too long. Some revision of these courses resulted in their length being reduced as a consequence.

Citations Scopus - 6Web of Science - 8
2001 Whittle AJ, Burford RP, Hoffman MJ, 'Assessment of strength and toughness of modified PVC pipes', Plastics, Rubber and Composites Processing and Applications, 30 434-440 (2001)

A series of modified PVC pipes, with different concentrations of chlorinated polyethylene, was manufactured under carefully controlled processing conditions. The strength and toug... [more]

A series of modified PVC pipes, with different concentrations of chlorinated polyethylene, was manufactured under carefully controlled processing conditions. The strength and toughness of each pipe was measured by a variety of methods including uniaxial tensile strength, notched C-ring, essential work of fracture, strain energy release rate, fracture toughness, and impact tests. Over the range of compositions tested, all of the quantitative measures of toughness and strength suggest an approximately linear relationship with modifier concentration. For pipe of the dimensions used in this study, the yield strength is overestimated when determined via the net section stress on the notched C-ring.

Citations Scopus - 10Web of Science - 9
2001 Zimmermann A, Hoffman M, Emmel T, Gross D, Rödel J, 'Failure of metal-ceramic composites with spherical inclusions', Acta Materialia, 49 3177-3187 (2001)

In this work the development of cavities in spherical metal inclusions within a metal-ceramic composite and the subsequent influence upon the strength of the composite is investig... [more]

In this work the development of cavities in spherical metal inclusions within a metal-ceramic composite and the subsequent influence upon the strength of the composite is investigated. A model experiment is undertaken whereby 100 µm diameter spherical aluminium inclusions are placed within an Al2O3-Al interpenetrating network composite. The samples are then fractured at temperatures ranging from room temperature to just below the melting temperature of aluminium. It is found that fracture originates from the aluminium inclusions and that there is clear evidence of cavitation in the ductile inclusions which also shows that these cavities formed as a result of high triaxial stress during cooling as a part of the fabrication process. This observation is supported by a numerical model of the stress formation and cavity growth process within an inclusion during cooling. The model also provides information on the effect of initial cavity size and location. Comparisons of experimental f racture strength and toughness data indicate that the observed high strength of these composites is explained by crack growth resistance due to ductile ligament bridging. © 2001 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.

DOI 10.1016/S1359-6454(01)00222-1
Citations Scopus - 26Web of Science - 23
2001 Li QK, Zhang Y, Hoffman M, Chu WY, 'Molecular dynamics simulation of dealloyed layer-induced tensile stress in Cu3Au', JOURNAL OF UNIVERSITY OF SCIENCE AND TECHNOLOGY BEIJING, 8 295-298 (2001)
2000 Whittle AJ, Burford RP, Hoffman MJ, 'Influence of residual stress on the relationship between pipe pressure and C-ring tests', Polymer Engineering and Science, 40 2311-2316 (2000)

The effects of residual stress in modified poly(vinyl chloride) pipes upon the relationship between pressure tests and C-ring tests have been studied. A series of pressure tests w... [more]

The effects of residual stress in modified poly(vinyl chloride) pipes upon the relationship between pressure tests and C-ring tests have been studied. A series of pressure tests were carried out at different hoop stresses using both fixed-end and free-end enclosures. The C-ring test was used to determine the yield strength of the material as a function of time. The difference in behavior between the fixed end and free end configurations was less than predicted by the von Mises analysis assuming the only stresses in the pipe wall were generated by the applied internal pressure. Both configurations produced lower results than predicted on the basis of the C-ring tests. The residual stresses in the hoop and longitudinal directions were measured. Taking into account the residual and applied stresses, the von Mises criterion for yield was used to calculate the uniaxial yield stress of the material for both end enclosure configurations. The results were similar to the yield stress measured in uniaxial tension. The von Mises criterion for yield has been shown to provide an acceptable method of analysis of pressure tests with fixed and free end enclosures and the C-ring, when residual stress is taken into account.

DOI 10.1002/pen.11363
Citations Scopus - 4Web of Science - 5
2000 Zimmermann A, Hoffman M, Röel J, 'Fracture mode of alumina/silicon carbide nanocomposites', Journal of Materials Research, 15 107-114 (2000)

Computer simulations have been designed to elucidate the evolution of microcracking in a nanocomposite using appropriate material values for alumina and silicon carbide. These are... [more]

Computer simulations have been designed to elucidate the evolution of microcracking in a nanocomposite using appropriate material values for alumina and silicon carbide. These are compared to a single-phase material using elastic and thermal expansion coefficients for alumina. It is found that the region and the fracture mode where microcracking ensues are determined by the intensity and the length scale of the residual stress fields, which interact. Of specific interest are the region, fracture mode, and length of ensuing microcracks for materials with different inclusion locations (at the grain boundary or within the grain) and with different grain size to inclusion size ratios. © 2000 Materials Research Society.

DOI 10.1557/JMR.2000.0019
Citations Scopus - 4Web of Science - 3
2000 Whittle AJ, Burford RP, Hoffman M, 'Improvements to C-ring fracture toughness test for poly(vinyl chloride) pipes', Plastics, Rubber and Composites Processing and Applications, 29 417-419 (2000)

Examination of the published procedure for performing calculations on data obtained from the C-ring fracture toughness test for unplasticised poly(vinyl chloride) reveals a major ... [more]

Examination of the published procedure for performing calculations on data obtained from the C-ring fracture toughness test for unplasticised poly(vinyl chloride) reveals a major flaw. The dimensions of the specimens do not satisfy the ASTM criteria for plane strain conditions and correction factors are therefore introduced. However, there is an error in the calculation procedure, which results in variations in the severity of the test with pipe wall thickness. An improved approach is proposed and recommendations are made for changing the ISO/DIS 11673·2 test standard, to allow for variations in the yield strength of unplasticised poly(vinyl chloride) and to identify the calculated data as Kc rather than K1c. © 2000 IoM Communications Ltd.

2000 Boughton P, Gregory C, Sinclair H, Patrick S, Hoffman M, Bandyopadhyay S, 'Recent developments in water-based coatings for the transport industry', Surface Coatings Australia, 20-25 (2000)
2000 Barbieri L, D'Arrigo MC, Leonelli C, Siligardi C, Pellacani GC, Sorrell CC, et al., 'Effect of silicon carbide whisker reinforcement on CaO-ZrO2-SiO2 glass-ceramic system', BRITISH CERAMIC TRANSACTIONS, 99 274-277 (2000)
DOI 10.1179/096797800681081
Citations Scopus - 1
1999 Hoffman M, Roedel J, Skirl S, Zimmermann A, Fuller E, Mullejans H, 'Tailoring of an interpenetrating network ceramic/metal microstructure to improve strength: Al

Significantly improved mechanical properties may be obtained by producing ceramic matrix composites with an interpenetrating network microstructure. In this work a ceramic matrix ... [more]

Significantly improved mechanical properties may be obtained by producing ceramic matrix composites with an interpenetrating network microstructure. In this work a ceramic matrix with a metal toughening phase microstructure is presented. The material is processed by infiltrating a porous ceramic preform with molten metal. Significantly improved strength, relative to a pure ceramic, results. Specific examples of Al2O3/Al and Al2O3/Ni3Al will be shown. Due the vastly different thermal expansion coefficients of the ceramic and metal phases high residual stresses are formed during cooling following metal infiltration. In the case of an Al2O3/Al composite residual stresses of 100-250 MPa compression in the ceramic and 400-800 MPa tension in the metal will be presented which have been calculated and measured using neutron diffraction. The metal can withstand such high stresses due to the high mechanical constraint exerted on ligaments of <5 µm diameter, which is significantly less than a grain diameter. The effect of varying metal ligament size and metal content is shown Due to the low failure strain of the ceramic, relative to the metal, fracture originates at a microcrack in the ceramic. Compressive stresses in the ceramic phase, however, significantly hinder microcrack initiation and explain improvements in strength. It is shown that strength improvements are in excess of what may be explained in terms of a toughness increase consequent of the metal phase. Specific microstructural features, necessary for improvement of mechanical properties, will be outlined by comparing the Al and Ni3Al materials and also be considering different processing techniques.

Citations Scopus - 6
1999 Hoffman M, Skirl S, Pompe W, Rodel J, 'Thermal residual strains and stresses in Al2O3/Al composites with interpenetrating networks', ACTA MATERIALIA, 47 565-577 (1999)
DOI 10.1016/S1359-6454(98)00367-X
Citations Scopus - 66Web of Science - 56
1998 Zimmermann A, Hoffman M, Flinn BD, Bordia RK, Chuang TJ, Fuller ER, Rödel J, 'Fracture of alumina with controlled pores', Journal of the American Ceramic Society, 81 2449-2457 (1998)

Fracture from artificial spherical pores, as well as natural defects, in alumina in a grain-size range of 0.8-9.2 µm has been studied experimentally and compared with a fracture-m... [more]

Fracture from artificial spherical pores, as well as natural defects, in alumina in a grain-size range of 0.8-9.2 µm has been studied experimentally and compared with a fracture-mechanics model. Results from fracture-strength measurements have been combined with detailed fractographic analysis to elucidate the ensuing crack instability. Two existing models of possible crack configurations have been extended and contrasted. The semicircular crack as well as the circumferential crack both are described as flaws in the stress-concentrating field of a spherical pore. Surface correction terms afforded by the presence of the pore have been incorporated. A comparative computation shows that fracture occurs more likely from the semicircular crack configuration than the circumferential crack configuration.

Citations Scopus - 59Web of Science - 50
1998 Merkert P, Hoffman M, Rodel J, 'Detection of prefracture microcracking in Al2O3 by acoustic emission', JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 18 1645-1654 (1998)
DOI 10.1016/S0955-2219(98)00111-3
Citations Scopus - 8Web of Science - 7
1998 Skirl S, Hoffman M, Bowman K, Wiederhorn S, Rodel J, 'Thermal expansion behavior and macrostrain of Al2O3/Al composites with interpenetrating networks', ACTA MATERIALIA, 46 2493-2499 (1998)
DOI 10.1016/S1359-6454(98)80033-5
Citations Scopus - 74Web of Science - 65
1997 Hoffman M, Fiedler B, Emmel T, Prielipp H, Claussen N, Gross D, Rodel J, 'Fracture behaviour in metal fibre reinforced ceramics', ACTA MATERIALIA, 45 3609-3623 (1997)
DOI 10.1016/S1359-6454(97)00057-8
Citations Scopus - 27Web of Science - 22
1997 Hoffman M, Rödel J, 'Suggestion for mechanism of strengthening of nanotoughened ceramics', Journal of the Ceramic Society of Japan, 105 1086-1090 (1997)
Citations Scopus - 20Web of Science - 12
1996 Sternitzke M, Knechtel M, Hoffman M, Broszeit E, Rodel J, 'Wear properties of alumina/aluminum composites with interpenetrating networks', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 79 121-128 (1996)
DOI 10.1111/j.1151-2916.1996.tb07889.x
Citations Scopus - 53Web of Science - 45
1996 Hoffman MJ, Wakayama S, Kishi T, Mai YW, Kawahara M, 'Crack closure during cyclic fatigue in MG-PSZ ceramic as detected by acoustic emissions', NONDESTRUCTIVE CHARACTERIZATION OF MATERIALS VII, PTS 1 AND 2, 210-2 487-494 (1996)
DOI 10.4028/www.scientific.net/MSF.210-213.487
1995 HOFFMAN M, MAI YW, WAKAYAMA S, KAWAHARA M, KISHI T, 'CRACK-TIP DEGRADATION PROCESSES OBSERVED DURING IN-SITU CYCLIC FATIGUE OF PARTIALLY-STABILIZED ZIRCONIA', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 78 2801-2810 (1995)
DOI 10.1111/j.1151-2916.1995.tb08057.x
Citations Scopus - 13Web of Science - 11
1995 HOFFMAN MJ, MAI YW, DAUSKARDT RH, AGER J, RITCHIE RO, 'GRAIN-SIZE EFFECTS ON CYCLIC FATIGUE AND CRACK-GROWTH RESISTANCE BEHAVIOR OF PARTIALLY-STABILIZED ZIRCONIA', JOURNAL OF MATERIALS SCIENCE, 30 3291-3299 (1995)
DOI 10.1007/BF00349872
Citations Scopus - 12Web of Science - 11
1993 HOFFMAN MJ, LENTZ W, SWAIN MV, MAI YW, 'CYCLIC FATIGUE LIFETIME PREDICTIONS OF PARTIALLY-STABILIZED ZIRCONIA WITH CRACK RESISTANCE CURVE CHARACTERISTICS', JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 11 445-453 (1993)
DOI 10.1016/0955-2219(93)90021-I
Citations Scopus - 12Web of Science - 10
Show 205 more journal articles

Conference (53 outputs)

Year Citation Altmetrics Link
2018 Hinterstein M, Mgbemere HE, Hoelzel M, Adabifiroozjaei E, Sorrell C, Hoffman M, 'Influence of Microstructure on Symmetry Determination of Piezoceramics', ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES (2018)
DOI 10.1107/S2053273318091192
2017 Raju, Rajan G, Ellakwa A, Hoffman M, Shouha P, Farrar P, Gangadhara Prusty B, 'In-vitro investigation of S-2 glass fibre aspect ratio on flexure strength, hardness and wear performance of fibre reinforced flowable dental composites', 9th Australasian Congress on Applied Mechanics, ACAM 2017 (2017)

© 2017 National Committee on Applied Mechanics. All Rights Reserved. With the continuous increase in the life expectancy and changing food habits, studying the wear of human tooth... [more]

© 2017 National Committee on Applied Mechanics. All Rights Reserved. With the continuous increase in the life expectancy and changing food habits, studying the wear of human tooth is of primary importance. Fibre reinforced composites are gaining major market share among various restorative dental materials. The current experimental investigation on the flexure strength, hardness and wear performance of dental restorative composites is to understand the effect of S-2 glass fibres of low volume (5%) and aspect ratio (AR 50, 70 & 100) embedded dental resins. Specimens with nine dental systems were manufactured and tested. Flexural strength is characterised as per ISO-4049 standards and hardness by Vickers hardness. Wear investigation is carried out with a fixed load during a single test providing steady condition. Wear pattern is also analysed and micro-mechanical behaviour is investigated using laser Microscope and SEM. It is observed that inclusion of processed AR 70 S-2 glass fibres increases the mechanical properties of resin by 10.3%, 34.1% and 54.1% respectively for flexure modulus, flexure strength and Vickers hardness. Coefficient of friction for composite samples was evaluated to be around 0.65 compared with resin samples at 0.35. Fibre length of 0.35 mm (aspect ratio = 70) provided the best results which is also the critical fibre length.

2015 Nazir MT, Phung BT, Hoffman M, 'Effect of AC corona discharge on hydrophobic properties of silicone rubber nanocomposites', Proceedings of the IEEE International Conference on Properties and Applications of Dielectric Materials (2015)

© 2015 IEEE. In wet conditions, corona discharges may occur on composite insulator surfaces of well-designed power transmission equipment. Corona exposure gradually reduces the su... [more]

© 2015 IEEE. In wet conditions, corona discharges may occur on composite insulator surfaces of well-designed power transmission equipment. Corona exposure gradually reduces the surface hydrophobicity and degrades the polymer surface. Recently, much attention has been paid on improvement of corona surface resistance by dispersing nanofillers in the base polymer. This paper presents experimental investigations to understand how silica filler loading can affect hydrophobic properties of RTV silicone rubber nanocomposites under AC corona discharge. Nano precipitated SiO2 with size of ~20 nm was used as filler. Silicone rubber nanocomposites with different nano SiO2 loading by weight were fabricated using mechanical stirring and ultrasonic water bath methods. A point-to-plane electrode geometry housed in a glass chamber was used to produce corona discharge at standard atmospheric pressure. The nanocomposite samples were placed between the electrodes, in direct contact with the plane electrode (ground) but separate from the point electrode by a fixed 5 mm air gap. The changes in hydrophobicity of test samples as a function of corona exposure time were determined by measuring the water static contact angle with a goniometer. The surface free energies of nanocomposite samples were calculated by considering the static contact angles of water and diiodomethane in relation to corona exposure duration. The surface morphology of nanocomposite samples was also studied by means of Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).

DOI 10.1109/ICPADM.2015.7295296
Citations Scopus - 11Web of Science - 11
2015 Hinterstein M, Hoelzel M-K, Rouquette K, Knapp M, Ehrenberg H, Hoffman M, 'Kinetics of strain mechanisms in functional materials: Stroboscopic powder diffraction on piezoceramics', ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES (2015)
DOI 10.1107/S2053273315098988
2015 Hang T, Glaum J, Phung BT, Hoffman M, 'Partial Discharge Characteristics of Piezoelectric Ceramics under Bipolar and Unipolar Applied Voltages', 2015 IEEE 11TH INTERNATIONAL CONFERENCE ON THE PROPERTIES AND APPLICATIONS OF DIELECTRIC MATERIALS, Sydney, AUSTRALIA (2015)
2012 Luo Z, Pojprapai S, Glaum J, Hoffman M, 'Electrical fatigue-induced cracking in lead zirconate titanate piezoelectric ceramic and its influence quantitatively analyzed by refatigue method', Journal of the American Ceramic Society (2012)

Lead zirconate titanate (PZT) is one of the most commonly used piezoelectric ceramics. The major causes of its electrical fatigue are suggested to be domain pinning and cracking. ... [more]

Lead zirconate titanate (PZT) is one of the most commonly used piezoelectric ceramics. The major causes of its electrical fatigue are suggested to be domain pinning and cracking. However, their contributions to fatigue have never been quantitatively compared. This study focuses on the electrical fatigue-induced microstructure damage in the near-electrode regions of PZT and uses a refatigue method to determine quantitatively the contribution of the cracking mechanism to electrical fatigue. It is shown that during bipolar electrical cycling, a large number of cracks are initiated in the samples, and the cracking is particularly concentrated in the near-electrode regions. So the loss of piezoelectric properties can be partially restored by removing such regions. For a particular fatigue stage, the cracking mechanism contributes significantly more to the electrical fatigue than the domain pinning mechanism. © 2012 The American Ceramic Society.

DOI 10.1111/j.1551-2916.2012.05232.x
Citations Scopus - 11Web of Science - 11
2012 Idris M, Vodenitcharova T, Hoffman M, 'Metal foam sandwich composites: Contact damage, remnant bending strength and energy absorption', Proceedings of the International Conference on Advanced Materials, Isfahan, Iran (2012)
2012 Thongmee N, Watcharapasorn A, Hoffman M, Jiansirisomboon S, 'Ferroelectric properties of Pb(Zr0.52Ti0.48)O-3-Bi3.25La0.75Ti3O12 ceramics', CERAMICS INTERNATIONAL, Jeju, SOUTH KOREA (2012)
DOI 10.1016/j.ceramint.2011.04.084
Citations Scopus - 3Web of Science - 2
2011 Calvert K, Trumble K, Chandrasekar S, Hoffman M, 'Ultrafine-grained commercially pure titanium and microstructure response to hydroxyapatite coating methods', Ceramic Transactions (2011)

Hydroxyapatite coating of orthopaedic implant materials generally involves high temperature plasma spray, which can initiate recrystallization and/or grain growth in ultrafine-gra... [more]

Hydroxyapatite coating of orthopaedic implant materials generally involves high temperature plasma spray, which can initiate recrystallization and/or grain growth in ultrafine-grained (UFG) titanium. Therefore, two alternative low-temperature hydroxyapatite coating methods (sol-gel spin coating followed by calcination (325-450°C) and anodization followed by hydrothermal processing (200-225°C)) are also investigated in terms of coating quality and thermal stability of the UFG titanium substrate. Plasma spray produced a crystalline coating ~38 µm thick with essentially no influence on the UFG titanium substrate. Sol-gel coating followed by calcination resulted in highly variable coatings with recrystallization and grain growth in the ultrafine grained titanium substrate. Anodization followed by a controlled hydrothermal process resulted in a homogeneous, roughened and porous coating integrating Ca and P ions into the Ti substrate. This work presents a unique hydrothermal processing route for conversion of the anodized precursor film. The underlying UFG Ti substrate was not influenced by the hydrothermal processing.

Citations Scopus - 2
2011 Kemal I, Whittle A, Burford R, Vodenitcharova T, Hoffman M, 'PVC-CaCO

PVC nano-CaCO3 composites have been successfully produced in the laboratory using two-roll mills or using sophisticated surface treatment method. The methods, however, are not acc... [more]

PVC nano-CaCO3 composites have been successfully produced in the laboratory using two-roll mills or using sophisticated surface treatment method. The methods, however, are not acceptable for commercial PVC processing. Thus, another approach needs to be developed to commercially produce PVC nanocomposites. This study focusses on the effect of the addition of titanate coupling agents on the mechanical properties of PVC nano-CaCO3 composites. The titanate is introduced into the PVC nanocomposite through an in-situ coupling technique, which is easily adapted to existing PVC manufacturing processes with minor modifications. The composites' morphology and the mechanical properties are also examined in this study.

Citations Scopus - 2
2011 Tang GCH, Hoffman M, Yan J, Zakaria QM, Lapovok R, 'Fatigue crack growth in ultrafine grained aluminium alloy', Materials Science Forum (2011)

The microstructure, fatigue crack growth behaviour and hardness of ultra fine grained 6061 aluminium alloy obtained by equal angle channel processing was studied. ECAP resulted in... [more]

The microstructure, fatigue crack growth behaviour and hardness of ultra fine grained 6061 aluminium alloy obtained by equal angle channel processing was studied. ECAP resulted in significant grain refinement down to the sub micron level and corresponding increase in hardness. Results point to a similar fatigue threshold stress intensity range and fatigue crack growth rates for 1, 2, 4 and 6 passes of ECAP. © (2011) Trans Tech Publications.

DOI 10.4028/www.scientific.net/MSF.690.254
2010 Wattanasakulpong N, Prusty BG, Kelly DW, Hoffman M, 'A theoretical investigation on the free vibration of functionally graded beams', Civil-Comp Proceedings (2010)

An improved third order shear deformation theory derived from elasticity theory is presented to analyse free vibration of functionally graded beams. A power law distribution is us... [more]

An improved third order shear deformation theory derived from elasticity theory is presented to analyse free vibration of functionally graded beams. A power law distribution is used to describe the variation of volume fraction of material compositions. The Ritz method is adopted to solve the governing equation in the form of an eigenvalue problem. All types of general boundary conditions are investigated in this paper. Convergence studies of this solution method are presented in order to achieve the results and define the accuracy. The numerical results are compared with the published results based on the first order shear deformation theory. © Civil-Comp Press, 2010.

2010 Singh RK, Zhou Z, Li LKY, Munroe P, Hoffman M, Xie Z, 'Design of functionally graded carbon coatings against contact damage', Thin Solid Films (2010)

Three different functionally graded amorphous carbon (a-C) thin films were deposited on to aluminium substrates using a closed-field unbalanced magnetron sputtering ion plating me... [more]

Three different functionally graded amorphous carbon (a-C) thin films were deposited on to aluminium substrates using a closed-field unbalanced magnetron sputtering ion plating method. The closed-field configuration prohibits the loss of secondary electrons and consequently enhances the plasma density significantly. The functional gradient of the a-C films was achieved by varying the bias voltage linearly during deposition. Three graded a-C systems possessing different variations in Young's modulus were deposited with the highest Young's modulus at the (i) top surface, (ii) interface or (iii) middle of the film. Of the three systems investigated, the one with the highest Young's modulus at the middle of the film thickness was found to exhibit significantly lower levels of cracking at higher indentation depths. Finite element models that included an embedded ring crack controlled by cohesive zone elements were developed to clarify the effect of ring cracks on the deformation of the films. This study provides guidance for the design of functionally graded coatings against contact damage. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

DOI 10.1016/j.tsf.2010.05.109
Citations Scopus - 21Web of Science - 21
2010 Hoffman M, 'Modeling the mechanics of CNTs in an elastic matrix', India (2010)
2009 Kabir KR, Vodenitcharova T, Hoffman M, 'Structural response of aluminium foam hybrid sandwich panels under three-point bending loading', International Journal of Modern Physics B (2009)

The present study focuses on the structural response of sandwich panels consisting of a commercial closed-cell foam core and thin aluminium sheet skins under static three-point be... [more]

The present study focuses on the structural response of sandwich panels consisting of a commercial closed-cell foam core and thin aluminium sheet skins under static three-point bending loading. Panels of different thicknesses and span lengths were tested, and the influence of the foam density, core thickness and skin type on the response was revealed. The failure modes in bending were greatly dependent on the span length but independent on the foam thickness. For short spans, the deformed shape at failure was asymmetric, as opposed to a symmetric mode for long spans. The density and thickness of the foam core, the presence of reinforcing face sheets and the beam span determined the failure load and bending strength of the sandwich panels. © World Scientific Publishing Company.

Citations Scopus - 6Web of Science - 3
2009 Kabir KR, Vodenitcharova T, Hoffman M, 'Residual strength in bending of damaged hybrid sandwich panels with an aluminium foam core', ICCM International Conferences on Composite Materials (2009)

Aluminium foam-cored sandwich panels were subjected to indentation and subsequently tested in four-point bending. The bending strength, failure modes and the deformation behavior ... [more]

Aluminium foam-cored sandwich panels were subjected to indentation and subsequently tested in four-point bending. The bending strength, failure modes and the deformation behavior were studied and compared with those of undamaged panels. It was found that the localised damage does not have a considerable effect on the failure modes and limit loads.

Citations Scopus - 1
2009 Hoffman M, Kemal I, Samat N, Burford R, Whittle A, 'PVC-based polymer nanocomposites: Processing, fracture and cyclic fatigue', ICCM International Conferences on Composite Materials (2009)

Nanoparticulate calcium carbonate was mechanically combined with PVC in varying volume fractions. The bonding strength between the particulate phase and the matrix was also varied... [more]

Nanoparticulate calcium carbonate was mechanically combined with PVC in varying volume fractions. The bonding strength between the particulate phase and the matrix was also varied. It was found that increasing the particulate content improves the toughness of the composite but this effect is reduced when interfacial bonding between the particles and matrix in improved; strength and stiffness show inverse behaviour. Modelling reveals that toughening is associated with hysteretic energy absorption processes associated with cavitation. Interestingly, the addition of nanoparticulate phase has no noticeable effect upon cyclic fatigue crack growth.

2008 Samat N, Whittle A, Hoffman M, 'The frequency effects on fatigue threshold of PVC-M and PVC-U in air and water medium', STRUCTURAL INTEGRITY AND FAILURE, Perth, AUSTRALIA (2008)
DOI 10.4028/www.scientific.net/AMR.41-42.183
2008 Borrero-Lopez O, Hoffman M, Bendavid A, Martin PJ, 'Strength measurement in brittle thin films', FUNDAMENTALS OF NANOINDENTATION AND NANOTRIBOLOGY IV, Boston, MA (2008)
2007 Daniels JE, Finlayson TR, Studer AJ, Hoffman M, Jones JL, 'Time-resolved diffraction measurements of electric-field-induced strain in tetragonal lead zirconate titanate', JOURNAL OF APPLIED PHYSICS (2007)
DOI 10.1063/1.2720255
Citations Scopus - 39Web of Science - 39
2007 Idris MI, Vodenitcharova T, Hoffman M, 'Resistance of thin Al foam panels to deep indentation', PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3, Cheju Isl, SOUTH KOREA (2007)
DOI 10.4028/www.scientific.net/MSF.561-565.357
Citations Scopus - 1Web of Science - 1
2007 Idris MI, Vodenitcharova T, Hoffman M, 'Contact damage response of carbon fibre skin/closed-cell aluminium foam sandwich composites', ICCM International Conferences on Composite Materials (2007)

The contact damage response of sandwich composites made of closed-cell aluminium foam core (ALPORAS) and carbon fibre skin has been experimentally investigated. Quasi-static inden... [more]

The contact damage response of sandwich composites made of closed-cell aluminium foam core (ALPORAS) and carbon fibre skin has been experimentally investigated. Quasi-static indentation tests on a series of core thicknesses were undertaken with indenters of different diameters. The behaviour of the damaged samples was then studied in four-point bending. It was shown that the contact damage on the surface of the sandwich samples is dependent only on the indenter diameter but independent of the sample thickness. The remnant compressive/tensile strength was also assessed. The results revealed that the undamaged samples exhibit higher strength than the damaged samples.

2006 Allen B, Crosky A, McAlpine I, Hoffman M, Munroe P, 'A blended approach to collaborative learning: Can it make large group teaching more student-centred?', WHO'S LEARNING? WHOSE TECHNOLOGY?, PROCEEDINGS, VOLS 1 AND 2, Univ Sydney, Ctr Res Comp Supported Learning & Cognit, Sydney, AUSTRALIA (2006)
Citations Scopus - 9Web of Science - 7
2006 Lok-Wang M, McGrouther D, Munroe P, Cairney J, Hoffman M, 'Three dimensional imaging of cracking in berkovich indented thin film coatings', TMS Annual Meeting (2006)

The use of a dual beam focused ion beam instrument is described for analysis of cracks induced using a Berkovich indenter in a TiN coating applied to a steel substrate. Convention... [more]

The use of a dual beam focused ion beam instrument is described for analysis of cracks induced using a Berkovich indenter in a TiN coating applied to a steel substrate. Conventional 2-dimensional characterization of the deformation microstructure is shown to be very location specific. By contrast, 3-dimensional visualizations, based on data acquired using a dual beam focused ion beam instrument, provide detailed information on the nature of the cracks which form under this type of loading.

2006 Jones JL, Hoffman M, Shelley WF, 'R-curve and stress-strain behavior of hard and soft PZT ceramics', Ceramic Transactions (2006)

The change in fracture toughness as a function of crack extension (R-curve) is measured and compared in both hard and soft lead zirconate titanate (PZT) ceramics using compact ten... [more]

The change in fracture toughness as a function of crack extension (R-curve) is measured and compared in both hard and soft lead zirconate titanate (PZT) ceramics using compact tension geometry. The soft PZT ceramic exhibited an initial fracture toughness of 0.70 MPa·m 1/22 and an increase in toughness of 0.66 MPa·m 1/2 while the hard PZT ceramic exhibited an initial fracture toughness of 0.78 MPa·m 1/2 and an increase in toughness of 0.10 MPa-m 1/2. The distinctive R-curve behavior of each composition is interpreted with respect to mechanical stress-strain results obtained using 4-point bending geometry. The intrinsic fracture toughness and extension toughening enhancement are correlated with bending strength and remanent strain, respectively.

2006 Jones JL, Hoffman M, 'Micro-Raman spectroscopy of a vickers indent on soft PZT', Ceramic Transactions (2006)

Raman scattering has proven valuable in eliciting phase transitions in lead zirconate titanate ceramics. However, its use as a quantitative tool for spatially characterizing local... [more]

Raman scattering has proven valuable in eliciting phase transitions in lead zirconate titanate ceramics. However, its use as a quantitative tool for spatially characterizing local strains and texture has yet to be fully optimized. This paper demonstrates that domain switching and microstrain surrounding a Vickers indent are manifested as changes in mode-specific intensities and Raman shifts. The intensity of the 265 cm-1 and 600 cm-1 modes increase inside the indent as a result of an increase in orientations of the corresponding bonds that are parallel to the indented surface.

2006 Furukawa T, Michopoulos JG, Hoffman M, 'Regularised identification of material constants using multi-objective gradient-based optimisation method', Fracture of Nano and Engineering Materials and Structures, Greece (2006)
2005 Xie ZH, Hoffman M, Moon RJ, Munroe PR, Cheng YB, 'Effect of microstructure on sliding wear of Ca alpha-sialon ceramics', HIGH-PERFORMANCE CERAMICS III, PTS 1 AND 2, Shenzhen, PEOPLES R CHINA (2005)
DOI 10.4028/www.scientific.net/KEM.280-283.1253
Citations Scopus - 4Web of Science - 4
2005 Tilbrook M, Rutgers L, Moon R, Hoffman M, 'Fracture and fatigue crack propagation in graded composites', FUNCTIONALLY GRADED MATERIALS VIII, Leuven, BELGIUM (2005)
DOI 10.4028/www.scientific.net/MSF.492-493.573
Citations Scopus - 5Web of Science - 6
2004 Moon RJ, Xie ZH, Hoffman M, Munroe PR, Cheng YB, 'Application of focused ion beam miller in indentation fracture characterization', INDENTATION TECHNIQUES IN CERAMIC MATERIALS CHARACTERIZATION, Nashville, TN (2004)
Citations Scopus - 1Web of Science - 1
2004 Hoffman M, Xie Z, Bendavid A, Martin P, 'Deformation Mechanism of Hard Coatings', Kolkata, India (2004)
2004 Hoffman M, Tilbrook MT, 'Implementation of the local symmetry criterion for crack-growth simulations', Brisbane, Qld (2004)
2004 Furukawa T, Hoffman M, 'Inelastic finite element analysis using implicit material modelling', Beijing, China (2004)
2004 Tilbrook MT, Rutgers LJ, Moon RJ, Hoffman M, 'Effective crack-propagation resistance under monotonic and cyclic loading', Brisbane, Qld (2004)
2002 Cheng YB, Xie ZH, Hoffman M, Munroe P, 'Microstructural tailoring and mechanical properties of Ca a-sialon ceramics', Key Engineering Materials (2002)

The microstructure of Ca a-sialon ceramics can be tailored via the control of sintering conditions. This provides an excellent opportunity for studying the effect of microstructur... [more]

The microstructure of Ca a-sialon ceramics can be tailored via the control of sintering conditions. This provides an excellent opportunity for studying the effect of microstructure on mechanical properties of ceramics. In this paper, a new approach to tailoring the microstructure of a selected Ca a-sialon composition is firstly presented. The process of microstructural evolution was analyzed in light of the relationship between the sintering parameters and the nucleation and growth rates. Secondly, mechanical properties of the Ca a-sialon composition, including wear resistance, were investigated in terms of microstructural variation. Fine-grained microstructure exhibited higher hardness, but lower fracture toughness and wear resistance, compared to large elongated microstructure. Crack bridging was the main toughening mechanism in the Ca a-sialon composition. Both hardness and fracture toughness played important roles in the control of Ca a-sialon wear resistance.

Citations Scopus - 1
2002 Hoffman M, Tilbrook MT, Moon RJ, 'Crack Propagation in Graded Alumina-polyester Composites', Perth, WA (2002)
2002 Ho T, Munroe PR, Crosky AG, Hoffman M, 'Materials engineering tutorials for architecture students using computer-aided learning', Canberra, ACT (2002)
2001 Moon R, Hoffman M, Rodel J, Hilden J, Blanton W, Bowman K, Trumble K, 'A weight function analysis of R-curve behavior in gradient alumina-zirconia composites', FUNCTIONALLY GRADED MATERIALS 2000, ESTES PK, CO (2001)
Citations Web of Science - 1
2001 Hoffman M, 'Effect of Crack Bridging Ligaments upon Crack Kinking in Graded Interfaces', London, UK (2001)
2001 Hoffman M, Moon RJ, Hilden J, Blanton W, Bowman K, Trumble K, 'A Weight Function Analysis on Gradient Alumina-Zirconia Composites', Westerville, Ohio (2001)
2001 Hoffman M, Munroe PR, Xie Z, 'Friction and Wear of a-Sialon Ceramics', Melbourne, Vic (2001)
2001 Hoffman M, Mubaraki B, Sternitzke M, 'Sliding Wear Behaviour of SiC-Alumina Nanocomposites', Melbourne, Vic (2001)
2000 Box VJ, Munroe PR, Crosky AG, Hoffman M, Krauklis P, Ford RA, 'Increasing student participation in a first year materials engineering service subject taken by mechanical engineers', Brisbane, Qld (2000)
2000 Boughton P, Gregory C, Patrick S, Sinclair H, Hoffman M, Bandyopadhyay S, 'Recent developments in water-based coatings for the transportation industry', Sydney, NSW (2000)
2000 Moon R, Hoffman M, Rodel J, Hilden J, Blanton W, Bowman K, Trumble K, 'A weight function analysis of R-curve behavior', Colorado (2000)
1999 Hoffman M, Roedel J, Skirl S, Zimmermann A, Fuller E, Mullejans H, 'Tailoring of an interpenetrating network ceramic metal microstructure to improve strength: Al2O3/Ni3Al and Al2O3/Al', NOVEL SYNTHESIS AND PROCESSING OF CERAMICS, KURUME, JAPAN (1999)
DOI 10.4028/www.scientific.net/KEM.159-160.311
Citations Web of Science - 5
1999 Hoffman M, Roedel J, Skirl S, 'Time-Dependent Thermal Deformation in Interpenetrating Network Ceramic/Metal Composites', Beijing, China (1999)
1998 Hoffman M, 'Metal/ceramic composites with an interpenetrating network structure', Wollongong, NSW (1998)
1997 Hoffman M, Skirl S, Pompe W, Rodel J, 'Fracture initiation in alumina/aluminium composites: Effect of residual stresses', Sydney, NSW (1997)
1995 Hoffman MJ, Wakayama S, Mai YW, Kishi T, Kawahara M, 'Cyclic fatigue mechanisms in partially stabilised zirconia', ASTM Special Technical Publication (1995)

Cyclic fatigue crack growth rate and crack resistance curve testing were undertaken on 6 different grades of Mg-PSZ. The width of the transformation zone at the flanks of the crac... [more]

Cyclic fatigue crack growth rate and crack resistance curve testing were undertaken on 6 different grades of Mg-PSZ. The width of the transformation zone at the flanks of the cracks was determined using Raman spectroscopy and, combined with R-curve toughening values, used to ascertain the level of crack-tip shielding during cyclic fatigue crack growth and hence the crack-tip stress intensity factor amplitude. By normalising the crack-tip stress intensity factor amplitude with the intrinsic toughness of the material, it was found that the cyclic fatigue threshold stress intensity factor was independent of the extent of crack-tip shielding and a function of the stress intensity factor at the crack tip. In situ SEM observations of cyclic fatigue revealed crack bridging by uncracked ligaments and the precipitate phase. Under cyclic loading the precipitate bridges were postulated to undergo frictional degradation at the precipitate/matrix interface with the degree of degradation determined by the cyclic amplitude. Acoustic emission testing revealed acoustic emissions at three distinct levels during the loading cycle: firstly, near the maximum applied stress intensity factor caused by crack propagation; secondly, at the mid-range of the applied stress intensity factor attributed to crack closure near the crack tip, presumably as a result of transformation induced dilation; and thirdly, intermittently near the base of the loading cycle as a result of fracture surface contact due to surface roughness at a significant distance behind the crack tip. Crack closure near the crack tip due to dilation is proposed to significantly reduce the crack tip stress intensity factor amplitude and hence the degree of cyclic fatigue.

1995 Hoffman M, Sternitzke M, Rodel J, Brook R, 'Fracture mechanisms in a strengthened nano-toughened alumina/silicon carbide composite'', Karlsruhe, Germany (1995)
1993 Hoffman M, Mai YW, 'The Effects of Material Microstructure on Cyclic Fatigue Crack Growth in Transformation-Toughened Ceramics', Tokyo, Japan (1993)
1992 Hoffman M, Dauskardt RH, Mai YW, Ritchie RO, 'A Review of the Mechanics and Mechanisms of Cyclic Fatigue-Crack Propagation in Transformation-Toughened Zirconia Ceramics', Melbourne, Vic (1992)
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News

University of Newcastle and TAFE NSW join forces for stronger Hunter and Central Coast post-COVID recovery

June 5, 2020

The University of Newcastle and TAFE NSW have committed to strengthening their 30-year partnership to ensure people in the Hunter and on the Central Coast can maximise their education options and be seamlessly supported as they enter tertiary education, re-train or up-skill following COVID-19.

New Deputy Vice-Chancellor (Academic) joins in 2020

December 12, 2019

Professor Mark Hoffman will join the University of Newcastle's executive leadership team as Deputy Vice-Chancellor (Academic) in March 2020.

Professor Mark Hoffman

Position

Deputy Vice-Chancellor (Academic) and Vice-President
Office of the DVC Academic
Office of the Deputy Vice-Chancellor (Academic)
Academic Division

Contact Details

Email mark.hoffman@newcastle.edu.au
Phone (02) 4921 5114
Mobile 0403830634

Office

Room CH-310
Building Chancellery
Location Callaghan
University Drive
Callaghan, NSW 2308
Australia
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