(85d) On the Numerical Calibration of Discrete Element Models for the Simulation of Bulk Solids

Due to the rapid increase of the computational power direct particle simulations, such as Discrete Element Simulations, become increasingly popular in the field of bulk solids handling and processing. Such application require the calibration of microscopic parameters, such as particle stiffness and inter particle friction, in order to fit the macroscopic numerical behaviour, e.g. stress-strain-behaviour, measured on real experiments. Thereby it is of greater importance to cover all relevant micro-mechanical aspects of bulk solids models in principle than modelling only a small subset of properties extremely accurate. The exact representation of particle shapes, for instance, appears to be of minor importance as their effects can be represented by contact laws. In particular for applications with bulk solids exposed to high shear movement, rolling friction caused by contact deformation and asperities on the particle surface becomes very important. Often yield loci obtained from shear tests are used for the calibration of numerical models (see figure, cohesion arises from liquid bridges and will be discussed briefly). However, because both Coulomb friction and rolling friction influence the internal friction angle on the macroscopic scale shear tests are not sufficient for a calibration procedure. The paper demonstrates that several pairs of Coulomb friction coefficients and rolling friction coefficients can be found that lead to the same macroscopic behaviour in a Jenike shear cell. Therefore, additional angle of repose tests were simulated and performed experimentally. The paper discusses comparisons of experiments and simulations and gives suggestions how calibrations should be carried out.