Rapeseed impact against a flat surface: Physical testing and DEM simulation with two contact models

Efficient application of a discrete element method (DEM) in modeling the behavior of granular materials requires contact models that reflect real behavior and realistic material parameters. The mechanical behavior of materials of biological origin is strongly influenced by the moisture content, which changes the surface and mechanical properties of seed endosperm and influences the bulk behavior. Laboratory tests and numerical DEM simulations were conducted to evaluate regions of validity for two basic contact models to describe the impact behavior of rapeseed at four moisture contents (5.5%, 7.5%, 14.7% and 34.0%). Seeds were allowed to free fall onto a flat surface from a height of 21 cm. Force-time waveforms were recorded using oscilloscope and rise and fall times were extracted for further analysis. DEM simulations were performed in which material parameters determined by a standard method fitted to two contact models were compared to experimental contact time Measurements. The elastoplastic model was suitable for impact of dry seeds, whereas the viscoelastic model gave a better fit for wet seeds. An efficient criterion for model selection was the ratio of the fall time to the rise time (TR) for the contact force-time characteristic. For TR<1 the elastoplastic model is suitable, whereas for TR>1 the viscoplastic model should be applied. (C) 2009 Elsevier B.V. All rights reserved.