Associate Professor Thomas Fiedler

This paper is concerned with sandwich foam tubes (SFTs), a recent type of sandwich structure containing metal syntactic foam (MSF). To create these structures, MSF is cast between thin-walled aluminium tubes in a single-step counter-gravity infiltration casting technique. Their mechanical properties and deformation mechanism are studied using quasi-static compression tests. For comparison, uniform MSFs and foam filled tube (FFT) structures are manufactured and tested alongside the SFTs. The deformation of the SFTs and FFTs is controlled by the symmetrical buckling of the tubes. A significant interaction effect between MSF and tubes is observed, i.e. the compressive strength of these structures exceeds the sum of their constituents. As a result, the specific energy absorption of the SFTs and FFTs increased compared with MSF samples.

The present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s.

This research study introduces a novel functionally graded metal syntactic foam. Counter-gravity infiltration casting is employed to manufacture MSF layers with dissimilar metallic matrices. Each layer combines expanded perlite particles with a different matrix alloy, i.e., ZA27 or pure aluminum. Dissimilar MSF layers are combined either during casting or using different joining techniques following manufacturing. The dissimilar matrices introduce a controlled gradient of the physical and mechanical properties of the resulting functionally graded foam material. Quasi-static compression testing shows that the initial deformation is controlled by the weaker aluminum syntactic foam layer. Following partial densification of this layer, deformation transitions toward the layer containing the higher strength ZA27 matrix alloy.

This study addresses the dynamic compression of functionally-graded (FG) metal syntactic foams (MSF). Cylindrical MSFs are manufactured by combining a ZA27 alloy with equal sized layers of expanded perlite (EP) and activated carbon (AC) particles. For comparison, uniform MSFs containing either particle type are manufactured with different aspect ratios. Samples are tested at the loading velocities 0.2 mm·s-1 (quasi-static) or 284 mm·s-1 (dynamic) to probe for changes of the deformation mechanism and effective mechanical properties. It is shown that uniform MSFs with a lower aspect ratio exhibit an increased overall strength. The underlying mechanism is a change of the shear failure mode, which has been closely studied by combining infrared (IR) imaging with dynamic compression. EP-MSFs exhibit a strength reduction at the higher loading velocity whereas AC-MSFs show no significant change. The dynamic deformation of FG-MSFs originates in the weaker EP layer and thus closely resembles the deformation behavior of the EP-MSFs. At higher strains, the deformation transitions to the AC layer and the stress-strain response changes accordingly.

This study investigates the heat transfer performance of a novel ZA27 metal foam heat exchanger. An open-celled metal foam is combined with a thin-walled copper tube in a single-step casting process. The heat transfer between two separated water streams flowing through the copper tube and foam, respectively, is measured and compared to an equivalent shell tube heat exchanger arrangement. Heat transfer enhancement of up to 71% and a heat transfer rate exceeding 30 kW are observed and attributed to the increased surface area of the metallic foam. However, overall performance was limited by the inefficient heat transfer between the internal mass stream and the copper tube.

Novel foam filled tubes were manufactured via a highly reproducible and cost effective in situ process. Stainless steel tubes were filled with ultralight porous expanded perlite particles and molten aluminium infiltrated the gaps between these particles. During casting, a ternary intermetallic phase was formed between the liquid aluminium and steel tube as a result of a chemical reaction. Quasi-static uni-axial compression testing was applied on the foam, empty tube, and foam-filled tube samples. Additional samples were subjected to quasi-static and dynamic three-point bending tests. The results of the quasi-static testing indicate that the foam filling improves the energy absorption capacity of tubes by 2.23 and 3.9 times for compressive and bending loading conditions, respectively. The dynamic bending tests indicate that both empty tubes and foam filled tubes exhibit a positive strain rate sensitivity. It is further shown that a larger tube wall thickness increases the energy absorption of both empty and foam-filled tubes. Foam-filling further increases the energy absorption capacity and, more importantly, the energy absorption efficiency. The impact of foam filling is more substantial in the case of tubes with lower thickness.

This paper addresses the dynamic mechanical characterisation of infiltration-cast aluminium foam. The material is produced by combining melt aluminium with salt precursors which are removed after solidification. The resulting aluminium foam allows controlled energy absorption and hence is of high interest for impact engineering applications at high strain rates. In this study, experimental and numerical analyses are combined to quantify its effective material properties and investigate relevant deformation mechanisms. First, uniaxial compression tests are conducted for both quasi-static and dynamic loading velocities. The comparison of the test results permits a direct evaluation of property changes due to the loading velocity. Under dynamic loading conditions, infrared imaging enables the localisation of concentrated plastification and provides important insight into the dominant deformation mechanism. Additional numerical finite element analyses were based on micro-computed tomography imaging of actual samples to accurately capture the complex foam geometry. Whenever possible, numerical findings were verified by comparison with experimental data. Both numerical results and infrared imaging indicate layer-wise collapse as the main deformation mode. Furthermore, the numerical results provide insight in the micro-deformation behaviour of analysed foam and allow additional evaluation of the strain rate sensitivity and the anisotropy of mechanical properties.

This paper introduces an improved method for the detailed geometrical characterization of perlite-metal syntactic foam. This novel metallic foam is created by infiltrating a packed bed of expanded perlite particles with liquid aluminium alloy. The geometry of the solidified metal is thus defined by the perlite particle shape, size and morphology. The method is based on a segmented micro-computed tomography data and allows for automated determination of the distributions of pore size, sphericity, orientation and location. The pore (i.e. particle) size distribution and pore orientation is determined by a multi-criteria k-nearest neighbour algorithm for pore identification. The results indicate a weak density gradient parallel to the casting direction and a slight preference of particle orientation perpendicular to the casting direction.

Abstract A novel metallic syntactic foam is produced using a counter-gravity infiltration casting method. To this end, expanded perlite particles are combined with an aluminium alloy matrix. This enables close control of geometry at a relatively low production cost. The mechanical properties of the material are studied using finite element analysis. Numerical calculation models are generated directly from micro-computed tomography in order to capture their complex internal geometry. For verification purposes, numerical results are compared with experimental measurements of similar samples where available. But in contrast to experimental testing the numerical analysis is non-destructive and hence allows the repeated testing of samples in multiple loading directions. Thus, material anisotropy can be investigated for the first time. To this end, the quasi-elastic gradient, the 1% offset yield stress and the plateau stresses are obtained from virtual compression tests in three perpendicular directions (one coincides with the casting direction). Results indicate a weak anisotropy of the mechanical properties.

This paper addresses the thermal testing of UniPore-paraffin composites for use as thermal capacitors. UniPore is a relatively new porous material with unidirectional pores formed by the explosive fusion of multiple thin copper pipes filled with paraffin. The current study investigates the suitability of this composite for transient thermal energy storage. The application demands both high thermal diffusivity and a large specific energy storage capacity. These requirements are met by the highly conductive copper and the phase change material paraffin, respectively. Combined experimental and numerical analyses are conducted towards the determination of temperature stabilization performance. Furthermore, key geometric criteria for the design of optimum UniPore structures as thermal capacitors are identified.

This paper addresses the analysis of expanded perlite/aluminum (EP/A356) syntactic foams under dynamic compressive loading conditions. Experimental and numerical analysis are conducted in order to determine compressive stress-strain response, effective material properties and deformation mechanisms. Foam samples are manufactured by combining A356 aluminum alloy with expanded perlite particles that introduce 60-65% porosity. Under compressive loading these pores gradually collapse resulting in an approximately constant macroscopic stress level of the syntactic foam. Testing at different compression velocities shows that the expanded perlite particles increase the compression resistance at higher strain rates. The effective material properties of the syntactic foam increase both with density and loading velocity. Infrared (IR) thermal imaging and finite element analysis allowed the independent identification of the dominant deformation mechanism: single struts that are parallel to the loading direction buckle and trigger the formation of multiple collapse bands that are approximately perpendicular to the loading direction.

This paper addresses the computation of the effective diffusivity in new bioactive glass (BG) based tissue engineering scaffolds. High diffusivities facilitate the supply of oxygen and nutrients to grown tissue as well as the rapid disposal of toxic waste products. The present study addresses required novel types of bone tissue engineering BG scaffolds that are derived from natural marine sponges. Using the foam replication method, the scaffold geometry is defined by the porous structure of Spongia Agaricina and Spongia Lamella. These sponges present the advantage of attaining scaffolds with higher mechanical properties (2¿4¿MPa) due to a decrease in porosity (68¿76¿%). The effective diffusivities of these structures are compared with that of conventional scaffolds based on polyurethane (PU) foam templates, characterised by high porosity (>90¿%) and lower mechanical properties (>0.05¿MPa). Both the spatial and directional variations of diffusivity are investigated. Furthermore, the effect of scaffold decomposition due to immersion in simulated body fluid (SBF) on the diffusivity is addressed. Scaffolds based on natural marine sponges are characterised by lower oxygen diffusivity due to their lower porosity compared with the PU replica foams, which should enable the best oxygen supply to newly formed bone according the numerical results. The oxygen diffusivity of these new BG scaffolds increases over time as a consequence of the degradation in SBF.

A novel filler material is introduced to produce high strength metal-matrix syntactic foam. Packed beds of pumice particles, a low-cost natural porous volcanic glass, with the size range of 2.8-4mm were infiltrated with molten aluminium alloy. The resulting syntactic foams were subjected to microstructural observations and chemical analysis. Furthermore, quasi-static compression testing was applied on heat treated samples. The material strength and the deformation mechanism under compressive loading of the pumice particles and foams were investigated. The results indicate that there is a limited chemical reaction between the particles and matrix. The pumice particles considerably enhance the strength of the foam and result in an average plateau stress of 68.25MPa and specific energy absorption of 24.8MJ/m3. Pumice particles show higher strength in the direction of tubular pores. The mechanical anisotropy of pumice particles is likely to cause a slight variation in the directional properties of the foams.

Abstract This paper addresses the thermal properties of syntactic metal foam made by embedding expanded perlite particles in A356 aluminium matrix. Lattice Monte Carlo (LMC) analyses are conducted to determine the thermal characterisation of the foam. For increased accuracy, the complex geometry of the metallic foam is captured by micro-computed tomography imaging. Using the resulting detailed geometric models, the effective thermal conductivity tensor is computed with possible thermal anisotropy taken into consideration. The numerical results are verified by comparison with experimental measurements. To this end, an improved steady-state method is used to correct for thermal contact resistance. Furthermore, the effective heat capacity, average density and thermal diffusivity of perlite - metal syntactic foam are determined.

Packed beds of expanded perlite (EP) particles with three different size ranges (1-1.4, 2-2.8, and 4-5.6. mm) have been infiltrated with molten Al to produce EP/A356 Al syntactic foam. A T6 heat treatment was applied to the foams. The effects of EP particle size on microstructural, geometrical, and mechanical properties of the foams were investigated. The EP particle size determines the number of cells across the sample diameter (7-25). It also influences the microstructural characteristics of the cell-wall alloy and the homogeneity of the cell-wall geometry. Enhanced microstructural characteristics and a greater geometrical homogeneity of the cell-wall in the case of smaller EP particles result in superior mechanical properties. The compressive deformation becomes more uniform by decreasing the EP particle size resulting in smoother and steeper stress-strain curves. As a result, these foams exhibit higher plateau stresses and improved energy absorption. The number of cells across the sample diameter does not have a significant effect on the mechanical properties of the samples considered.

This paper addresses the mechanical behavior of robocast PCL-Bioglass^® scaffolds. These structures can be used as 3rd generation implants in tissue engineering to support the regrowth of damaged tissue, in particular bone. After successful tissue regeneration the scaffolds slowly dissolve leaving no foreign material permanently inside the body. However, to avoid mechanical separation from surrounding tissue they must exhibit similar mechanical properties. The present study introduces a detailed numerical study focusing on the determination of effective mechanical material properties, their anisotropy, and mechanical degradation due to scaffold resorption. In order to accurately capture the complex scaffold geometry, micro-computed tomography scans of actual samples are conducted. The resulting three-dimensional data are directly converted into finite element calculation models. Numerical compressive tests of these unmodified models are repeated for three perpendicular directions to investigate mechanical anisotropy, after which the effect of scaffold degradation due to exposure to body fluid is simulated. To this end, two different resorption models, namely surface erosion and bulk degradation, are applied to the micro-computed tomography data. The modified geometry data are then converted into calculation models and numerical compression tests then allow the prediction of the mechanical properties of partially resorbed scaffolds.

Abstract This paper addresses the mechanical characterization of polycaprolactone (PCL)-bioglass (FastOs®BG) composites and scaffolds intended for use in tissue engineering. Tissue engineering scaffolds support the self-healing mechanism of the human body and promote the regrowth of damaged tissue. These implants can dissolve after successful tissue regeneration minimising the immune reaction and the need for revision surgery. However, their mechanical properties should match surrounding tissue in order to avoid strain concentration and possible separation at the interface. Therefore, an extensive experimental testing programme of this advanced material using uni-axial compressive testing was conducted. Tests were performed at low strain rates corresponding to quasi-static loading conditions. The initial elastic gradient, plateau stress and densification strain were obtained. Tested specimens varied according to their average density and material composition. In total, four groups of solid and robocast porous PCL samples containing 0, 20, 30, and 35% bioglass, respectively were tested. The addition of bioglass was found to slightly decrease the initial elastic gradient and the plateau stress of the biomaterial scaffolds.

This paper addresses the electrical and thermal contact resistance in metal foam-graphite assemblies considered for use in next generation air-cooled fuel cells as replacements of currently available water-cooled ones. Their successful application requires minimization of thermal and electrical contact resistance between components. The current study investigates the evolution of both resistances with increasing compressive force between metallic foam and graphite plates. Reducing these contact resistances through compressive force instead of brazing significantly reduces the manufacturing cost. Our results show that both electrical and thermal resistances monotonically decrease with increasing compressive force when moving from no compressive force to a slight one about 100 N (corresponding to a compressive stress of 0.01 MPa). Interestingly, compared with the thermal contact resistance, the electrical contact resistance shows more sensitivity to compressive force within this range of force. Furthermore, it has been noted that increases in compressive force beyond 300 N (i.e. 0.03 MPa) decrease the resistances only marginally. Electrical contact resistance was found to govern the total resistance of the metal foam-graphite assembly since electric bulk resistances are several orders of magnitude lower. Similar observations are made for thermal resistance where the minimum contact resistance exceeds the thermal resistance of the foam in our experiments. © 2014 Elsevier Ltd. All rights reserved.

The effective thermal conductivity of Cu-Fe and Sn-Al miscibility gap alloys over a range of temperatures and volume fractions was determined using the Lattice Monte Carlo method. The Cu-Fe system was found to have an effective conductivity predictable by the Maxwell-Eucken model. The Sn-Al system was not consistent with any empirical model analysed. The microstructures of physical samples were approximated using a random growth algorithm calibrated to electron or optical microscope images. Charts of effective conductivity against temperature for a number of volume fractions are presented for the two alloys. It was determined that the Cu-Fe alloy would benefit from an interstice type microstructure and the Sn-Al would be more efficient with a hard spheres type microstructure. More general conclusions are drawn about the efficiency of the two observed microstructures. © 2014 Elsevier Ltd. All rights reserved.

This paper addresses the numerical analysis of the mechanical properties of titania foam intended for use in tissue engineering scaffolds. Special focus is given to a PDLLA coating that has been shown to distinctly increase the mechanical strength of the scaffold. Micro-computed tomography (µCT) data of a real scaffold are obtained and converted into numerical calculation models. Finite element simulations are performed alternately with and without the PDLLA coating. In addition, a strut model containing a single micro-crack is analysed. Numerical results indicate that filling the crack with PDLLA significantly increases the strength of the strut by attenuating stress concentrations. © 2013 Elsevier Ltd. All rights reserved.

This paper addresses an innovative syntactic foam (SF) formed by counter-gravity infiltration of a packed bed of low-cost expanded perlite (EP) particles with molten A356 aluminium. The uniform distribution of EP particles in foams causes an even density throughout the height. Due to the low density (~0.18g/cm3) of EP, the average density of these foams is only 1.05g/cm3 which is considerably lower than most studied SFs. Owing to the high porosity of the filler material (~94%), the total porosity of the new foam reaches 61%. Microstructural observations reveal no sign of damage or unintended EP particle infiltration. EP shows a good wettability whilst essentially no reaction occurs at the EP-metal interface. Under compression, EP/A356 syntactic foam shows stress-strain curves consisting of elastic, plateau and densification regions. On account of its consistent plateau stress (average value 30.8MPa), large densification strain (almost 60%), and high energy absorption efficiency (88%) EP/A356 syntactic foam is an effective energy absorber. © 2014 Elsevier B.V.

This paper addresses the use of the Lattice Monte Carlo method for the thermal characterization of composite materials. An optimized approach that minimizes computational time is presented. The key aspect of the approach is the avoidance of the need to model the local thermal inertia. A combined finite element and Lattice Monte Carlo analysis is conducted on a model composite for a formal verification of the effective thermal diffusivity and conductivity calculated by the optimized Lattice Monte Carlo method. The effective thermal inertia is calculated separately by making use of the energy conservation law. © 2014 Elsevier Ltd. All rights reserved.

Tissue engineering scaffolds are designed to support tissue self-healing within physiological environments by promoting the attachment, growth and differentiation of relevant cells. Newly formed tissue must be supplied with sufficient levels of oxygen to prevent necrosis. Oxygen diffusion is the major transport mechanism before vascularization is completed and oxygen is predominantly supplied via blood vessels. The present study compares different designs for scaffolds in the context of their oxygen diffusion ability. In all cases, oxygen diffusion is confined to the scaffold pores that are assumed to be completely occupied by newly formed tissue. The solid phase of the scaffolds acts as diffusion barrier that locally inhibits oxygen diffusion, i.e. no oxygen passes through the scaffold material. As a result, the oxygen diffusivity is determined by the scaffold porosity and pore architecture. Lattice Monte Carlo simulations are performed to compare the normalized oxygen diffusivities in scaffolds obtained by the foam replication (FR) method, robocasting and sol¿gel foaming. Scaffolds made by the FR method were found to have the highest oxygen diffusivity due to their high porosity and interconnected pores. These structures enable the best oxygen supply for newly formed tissue among the scaffold types considered according to the present numerical predictions.

This paper addresses the mechanical properties of Corevo® aluminium foam. The effective Young's modulus, Poisson's ratio, and material yield stress are determined. To this end, samples are tested using uni-axial compressive testing. In addition, micro-computed tomography data of the complex material geometry are obtained and converted into finite element calculation models. The numerical analysis further enables the testing of mechanical material anisotropy and plastic deformation within the material's meso-structure. © 2013 Elsevier B.V. All rights reserved.

This paper reports on an investigation of the compressive properties of Corevo® foam. Corevo® foam is a cellular metal manufactured by the infiltration casting of salt dough with aluminium. Corevo® foam samples with different porosities are tested by using quasi-static compression loading. Their mechanical properties (i. e.: effective Young's modulus, Poisson's ratio, initial yield stress and material yield stress) are then compared to reveal the importance of the density difference. In addition, three-dimensional finite element analysis is performed on models generated from micro-computed tomography (µCT). The results of two different pore sizes are obtained and compared in the scope of this work. These numerical results are verified by comparison with the experimental analysis. Sound agreement is found. Numerical analysis in this work also includes the investigation of the mechanical material anisotropy and plastic deformation. © (2014) Trans Tech Publications, Switzerland.

Metallic hollow sphere structures constitute a new group of porous metals. They are in contrast to metallic sponges characterised by a defined cell respectively sphere geometry which yields to less scattering in material parameters. In the scope of this paper, the potential for lightweight construction of this material is analysed by means of the finite element method. In addition to macroscopic Young's modulus, the initial yield strength in dependence on the averaged structural density is determined.

The mechanical properties of periodic hollow-sphere structures are investigated numerically. Young's modulus and the Poisson ratio are determined in order to describe their linearly elastic behaviour. The initial compressive yield strength is also calculated. The spheres are located at the nodes of a cubic primitive lattice. The cohesion is achieved by an adhesive concentrated in the minimum gap between neighbouring spheres. The geometry of the structure is discretized based on regular hexahedral elements. This approach is much more time-consuming, but it is important in order to achieve a more accurate simulation of the nonlinear behaviour (e.g., plasticity) of such materials. © Springer Science+Business Media, Inc. 2006.

The application of cellular materials in load-carrying and security-relevant structures requires the exact prediction of their mechanical behavior, which necessitates the development of robust simulation models and techniques based on appropriate experimental procedures. The determination of the yield surface requires experiments under multi-axial stress states because the yield behavior is sensitive to the hydrostatic stress and simple uniaxial tests aim only to determine one single point of the yield surface. Therefore, an experimental technique based on a uniaxial strain test for the description of the influence of the hydrostatic stress on the yield condition in the elastic-plastic transition zone at small strains is proposed and numerically investigated. Furthermore, this experimental technique enables the determination of a second elastic constant, e.g., Poisson's ratio.

The classical assumption in solid materials, i.e. that the plastic behaviour is incompressible, does no longer hold in the case of cellular materials. The plastic behaviour is pressure-sensitive due to the cellular structure even when the pure base material is independent of the hydrostatic pressure in the plastic range. Therefore, the yield criterion needs to incorporate the hydrostatic pressure. In many cases, the yield criterion can be simplified to an additive form where an arbitrary scalar function weights the influence of the hydrostatic stress. The yield stress can be obtained from uniaxial tests but the determination of the weighting function for the hydrostatic stress requires the realisation of multi-axial stress states. This work presents two experimental procedures, i.e. an experiment under plane strain conditions and the axial compression, for the determination of the parameters of the yield criterion in the elasto-plastic transition zone. Furthermore, both experiments aim to determine a second elastic constant if for example Young's modulus is known from uniaxial compression tests. The proposed procedures are numerically applied to a material obeying the Deshpande-Fleck yield criterion. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

The numerical simulation of random cellular metals, e.g., metal foams, is still connected with many unsolved problems due to their stochastic structure. Therefore, a periodic model of cellular metals is developed and its mechanical behavior is investigated numerically under uniaxial and multiaxial stress states. The main advantage of the model is that a wide range of relative densities can be covered and that test specimens of the same geometry are possible to manufacture without oversimplifying their shape. The influence of different hardening behavior and different boundary conditions on the characteristics of the material is investigated. Furthermore, the effect of internal pore pressure on its uniaxial behavior and on the shape of yield surface are determined. © Springer Science+Business Media, Inc. 2005.

This paper is on the investigation of the orthotropic heat transfer properties of unidirectional fibre reinforced materials. The orthotropic effective thermal conductivity of such composite materials is investigated based on two different approaches: the finite element method as a representative for numerical approximation methods and an analytical method for homogenised models based on the solution of the respective boundary value problem. It is found that fibre reinforced composites possess strong orthotropic heat transfer properties, which are getting more distinctive with increasing deviation of the thermal conductivities of matrix and reinforcements. Furthermore, the effect of small perturbations of the periodic configuration of fibres in the matrix on the thermal conductivity is investigated. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The current paper addresses the thermal characterisation of Miscibility Gap Alloys (MGAs). These novel materials combine two immiscible metallic phases with different melting temperatures. The fusible phase (i.e. the phase with a lower melting temperature) acts as a phase change material that stores latent heat (in addition to sensible heat) thus optimising energy storage capacity. The second phase forms an enclosure and prevents the leakage of liquid material. Due to the high inherent thermal conductivity of metals, MGAs exhibit excellent thermal conduction in comparison to traditional phase change materials such as hydrate salts or paraffin. The combination of high energy storage and fast heat transfer makes MGA uniquely suited for use as thermal capacitors in applications like space heating, concentrated power generation or temperature stabilisation of sensitive equipment. The current paper determines the thermal properties of MGAs using Lattice Monte Carlo analysis combined with micro-computed tomography imaging.

In order to develop computational methods for determining the reaction of biological systems exposed to THz radiation, conventional approaches of numerical dosimetry have to be extended. The penetration depth of electromagnetic fields at THz frequencies is less than 1 mm and thus substantially smaller than for radio frequencies. In addition, the short wavelengths in this frequency range cause the necessity of high resolution models. Here, a selection of simulation models of the human skin and of the eye as well as of the excitation field are presented together with a proposal to assess the appropriate dielectric tissue parameters. © 2012 IEEE.

Composite materials offer for automotive applications the specific advantage of low constructive weight in combination with a high stiffness. For vibro-acoustic applications, especially the low structural weight leads to higher vibration amplitudes due to low forces of inertia and causes undesired sound radiation. A useful approach to eliminate these drawbacks and increase the structural damping without adding too much additional weight to the construction is the integration of viscoelastic damping layers in the composite materials during the manufacturing process. In the presented experimental study, different types of viscoelastic Ethylene-Propylene-Dien-Monomer (EPDM) rubber sheets are integrated in the mid-plane of a reference laminate made from carbon textile-reinforced epoxy. The vibro-acoustic properties of the fibre-reinforced multilayered composites - absorption coefficient, sound reduction index, dynamic stiffness and material damping - were measured and compared. As expected, the integration of EPDM sheets in the composite leads to higher material loss factors. To identify the vibro-acoustically optimal position of the EPDM layer within the composite lay-up, special simulation methods suitable for composite materials have to be used.

This paper is on the investigation of adhesively bonded metallic hollow sphere structures, Two different approaches, namely experimental analysis and finite element calculations are applied and the findings of both attempts arc compared. In the scope of the numerical approach the influence of the mechanical properties of the adhesive on the mechanical response of the structure is analysed. Based on these results, suggestions for design parameters are derived.

Hollow sphere structures (HSS) constitute a group of innovative materials which are characterised by more constant material properties compared to classical cellular metals [1]. Their big potential lies within multifunctional applications where combinations of their properties yield symbiotic advantages. In the scope of this paper their effective thermal conductivity is investigated. In addition to the analysis of the dependency of this material parameter on the conductivities of the base materials and the sphere wall thickness, special focus is given to the influence of the morphology of joining.

The effective conductivity of 2D porous materials with temperature dependent matrix properties is investigated by two different approaches: namely, a numerical and an analytical method. A model with disjoint parallel cylindrical pores in a representative cell is considered. The numerical method is represented by the finite element method. In the scope of the analytical method, the nonlinear boundary value problem which describes conducting properties of the materials is solved by the methods of complex analysis, and the effective conductivity is represented in an explicit form via the solution of this problem. The values of the effective conductivity obtained by two these methods are compared.

This paper is on the geometrical effective thermal conductivity of hollow metal sphere structures. Two different technologies of joining, namely adhesive bonding and sintering, are considered. The spheres are arranged in the nodes of a cubic primitive lattice and connected by an adhesive layer, respectively directly joined by sintering. Furthermore, the influence of the cell wall thickness of the spheres on the thermal conductivity is investigated.

In this paper, the geometrical effective thermal conductivity of porous materials is investigated based on two different approaches: the finite element method as a representative for numerical approximation methods and an analytical method for 2D homogenised models based on a solution of the respective boundary value problem. It is found that the relative conductivity is practically independent of the specific shape or topology of the inclusions. Only the morphology (closed-cell or open-cell) of the structure slightly influences the conductivity. Furthermore, it is shown that a small perturbation of the circular inclusions of 2D models increases the effective conductivity.