SHEAR-INDUCED ANISOTROPY ANALYSIS OF CONTACT NETWORKS INCORPORATING PARTICLE ROLLING RESISTANCE

The macroscopic mechanical behaviour of granular materials is closely related to the fabric anisotropy of the contact networks. The interparticle contact system can be divided into different sub contact networks according to whether the contacts slide or not, rotate or not and the magnitude of interparticle contact forces. It is generally accepted that the mechanism of force transfer of different sub contact networks varies, which would result in the different contribution to the macroscopic mechanical responses. Based on the discrete element method (DEM), a series of conventional triaxial tests for granular materials with different rolling resistance coefficients \mu_r are carried out. The evolutions of the fabric tensor of different sub contact networks during shearing process are analyzed. The influence of rolling resistance coefficients on the evolution of contact normal and normal contact force anisotropy indexes of different sub contact networks is explored. The numerical results demonstrate that the evolutions of fabric tensors of rolling and non-rolling contacts are not independent and are affected by the sliding between particles. The non-sliding and the strong force related contact networks are the main force transfer structures of the granular system. The contact normal and normal contact force anisotropy indexes of the non-sliding contact networks increase with the increase of \mu_r, and the contribution of the non-sliding contact networks to the macro stress decreases with the increase of \mu_r. For the strong force contact networks, the contact normal anisotropy index increases with the increasing \mu_r while the normal contact force anisotropy index has no obvious change with the increase of \mu_r. The contribution of strong contact network to the macro stress is the same under different \mu_r.