基于接触价键的颗粒材料微观临界状态

用颗粒离散元法，分别对二维圆形、椭圆形颗粒体进行了双轴压缩数值模拟。微观尺度的变形是基于孔隙胞元和其中的变形来计算的，而单个孔隙胞元的变形通过周围颗粒的相对运动来计算。针对该方法提出了以接触价键（每个孔隙胞元的边数）来表征颗粒材料微观临界状态的理论。为了定义临界接触价键的极限值，分别讨论了摩擦系数较大、较小时的两种情况。文中给出了微观几何织构（包括接触价键、孔隙胞元的形状、孔隙比）随压缩变形的演变过程，比较了不同颗粒形状、颗粒间摩擦系数以及颗粒体的固结压力对颗粒体的微观力学性能的影响。计算结果表明，颗粒材料的微观临界状态并不是可以唯一表征的，而是受围压、摩擦系数，颗粒形状等参数的共同影响。

Microscopic critical state based on Valence of granular materials

Numerical simulations of two-dimensional circular and ellipsoid particulate arrays are carried out based on granular discrete element method. The microscale deformations are measured based on void cells and the deformations occur in them. Deformations within individual voids are computed from the relative motions of surrounding particles. Based on the deformation mechanism, a more physical theory of critical state is developed in terms of valence (number of edges per void cell). Two ultimate cases with large and small friction coefficients are analyzed to define the maximum critical valence. The effects of particle shape, interparticle friction and consolidation stress of the granular assembly on the microscopic fabrics are investigated. The simulation results show that the microscopic critical state can not be characterized by a unique parameter, but depends on the shape and surface characteristic of the individual particles and consolidation stress of the particulate assembly.