LAUSR

Abstract For impacts on plane surfaces (plates), the coefficient of restitution or more precisely, the energy dissipation due to elastic waves (Rayleigh, longitudinal, transverse and flexural waves) on the one hand and due to viscoelastic properties on the other hand is calculated, analysed and experimentally investigated. Models concerning elastic waves (Zener, Hunter) and their modifications introduced by us within our latest publications (Boettcher et al., 2016, 2017a, 2017b), which (like the majority of the models in literature) are related to spheres and parabolically impinging bodies, are briefly summarized and extended for the impact of cones to achieve a more realistic description of impact processes and a better understanding of the physical relations. The bending model of Zener is described on the basis of rheological models (contact model) and a simple, general viscoelastic model for a sphere is introduced. Furthermore, two different variants of a combined model are derived with which the coefficient of restitution based on flexural waves (inelasticity parameter λ) and viscoelastic properties (viscoelastic inelasticity parameter ξ) can be calculated. Likewise, analytically approximate solutions are derived. In chemical and process engineering, the proposed approach enables for instance a better description of the impact process between (elastic-plastic) granules or particles with viscous properties (e.g., γ-Al2O3 or synthetic granules) and thin apparatus walls at which flexural waves as well as viscous damping can depict a (decisive) role (fluidized bed, pneumatic conveying). First experimental evaluations show the extent to which viscoelasticity depends on the individual materials and the influence of viscoelasticity within the range of the (developing) flexural wave. The combined model shows a qualitative good agreement to the experimental measurements, but also an increasing deviation from the experimental values with increasing viscous damping.