考虑颗粒转矩的接触网络诱发各向异性分析

颗粒材料的宏观力学行为与接触网络的组构各向异性密切相关, 根据接触点的滑动与否、转动与否和强弱力情况, 可以将颗粒间的接触系统分为不同的子接触网络. 一般而言, 不同的子接触网络在颗粒体系中的传力机制不同, 对宏观力学响应的贡献也有不同. 采用离散单元法(discrete element method, DEM)模拟了不同抗转动系数$\mu_r$下颗粒材料三轴剪切试验, 分析了剪切过程中不同子接触网络的组构张量的演变规律, 并探究了颗粒抗转动效应对子接触网络各向异性指标演变规律的影响. 研究发现: 剪切过程中转动、非转动接触的组构张量变化不是独立的, 受到颗粒间滑动与否的影响; 非滑动、强接触网络是颗粒间的主要传力结构, 非滑动接触网络的接触法向和法向接触力各向异性均随$\mu_r$的增大而增大, 其对宏观应力的贡献程度随$\mu_r$的增大而减小;强接触网络的接触法向各向异性随$\mu_r$的增大而增大, 但法向接触力各向异性随$\mu_r$的增大无明显变化, 强接触网络对宏观应力的贡献程度在不同$\mu_r$情况下均相同. 

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 $\mu_r$.