Dr Klaus Thoeni

© 2019, Springer-Verlag GmbH Austria, part of Springer Nature. The normal coefficient of restitution (NCOR) is a useful index to quantify the energy dissipation during impact. This study presents experimental tests of marble spheres impacting a plate. The effects of the sphere diameter, elastic properties of the plate, impact velocity, and repeated impacts on the NCOR were investigated. Three fracture phases were observed: no macrocrack, macrocrack, and fragmentation. A clear influence of the propagation of the macrocracks on the NCOR was observed. Macrocracks also cause increased NCOR variability. The cumulative damage caused by macrocracks can affect the propagation of macrocracks and fragmentation. In the no macrocrack phase, the NCOR decreases with increasing velocity and with decreasing diameter, and the velocity effect of the NCOR is also related to the size of the marble sphere. The proposed average rate of contact stress correlates well with the NCOR and can describe fully the velocity and size effects of the NCOR, which provides a simple way to consider the complex velocity and size effects in rockfall simulations. The dissipation caused by microcracks and viscosity can be considered simultaneously through the average rate of contact stress. The marble sphere NCOR decreases with increasing elasticity modulus of the plate, and this conclusion is verified by the elastic-perfectly plastic contact theory. Finally, viscoelastic contact theory is used to describe the NCOR, which proves that the decrease in the NCOR with decreasing diameter is reasonable and can be used to predict a decrease in the NCOR with an increase in velocity.

© 2018 Taylor & Francis Group, London, UK. The design strategies of metallic cortical meshes used for slope protection are mostly linked to the application of empirical and semi-empirical methods. This limitation is due to the difficulties in representing such complex large-deformation rock-soil-structure interaction problems: the intrinsic complexities of these structures is combined with the difficulties in describing the geometry both the mechanical and physical properties of the rock and soil behind. The Discrete Element Method proved their effectiveness in describing the non-linear and large strain behaviour of the soil, and recently also the mechanical response of steel wire meshes which are represented as regular patterns of remote interactions between nodes. In this work, a discrete element model of a double-twisted hexagonal wire mesh is calibrated on the base of experimental tensile tests on two wire types. The validation of the model is performed using the results of a standard punch test. The same mesh is then loaded by a granular layer constituted by discrete element particles mimicking the soil earth pressure. A comparison between the two load types is discussed with reference to the force-displacement curve and the distribution of the tensile stresses on the mesh panel. The effect of the boundary conditions is also analysed.