Numerical stress analysis of granular material

The knowledge about granular materials is rather limited compared to the respective information on the solids, while a unified theory encompassing all granular material phenomena has not been created yet [1]. Despite the fact that granular material is the discontinuous media its behavior is commonly described by the continuum approach. Consequently, the definition of stresses in granular material is a controversial topic of mechanics [2, 3]. In particular, some researchers (e.g. [4]) claim that the stress tensor is asymmetric and the coupled stresses responding to the material instabilities, such as shear bending, exist. Others (e.g. [5]) affirm that stress asymmetry is not bound or can be negligible in practical predictions. The simplified continuum models are used to predict the pressure fields, especially those acting on the walls but they have serious drawbacks in evaluating the effects occurring on the particle level. Furthermore, the experimental stress investigations within the granular material are also complicated, requiring non-invasive and precise contact force measurements [6, 7]. An alternative is to perform DEM-based [8] simulations and then average the particle contact forces and their contact locations over the particular volumes. Such numerical studies based on the linkage of microscopic variables in discrete concept to the macroscopic variables in continuum approach can be found in e.g. [3], [9, 10]. In the current research, the numerical stress analysis of granular material, based on discrete particle model involving laws of single particle contact mechanics and the effects of friction as well as viscous damping forces is performed. Verification of the obtained results and their compatibility with well-known continuum-based indications are also demonstrated.