双轴压缩下颗粒物质剪切带的形成与发展

Development of shear band in a granular material in biaxial tests

本文采用离散元方法,研究了双轴压缩的颗粒体系在刚性边界约束下,局部剪切带的形成和发展过程,注重分析了细观的体积分数、配位数、颗粒旋转角度等参数以及力链结构形态的演变.并从颗粒体系jamming相图中J点附近的边壁压强和配位数随体积分数的标度规律出发,分析了剪切带内外的体积分数和配位数的变化.结果表明:剪切带形成于颗粒体系的塑性变形开始阶段,此时体系发生剪胀,颗粒体积分数减小,颗粒体系抵抗旋转的能力降低,开始出现细小剪切带,随着轴向应变的继续,细小剪切带发生连接,最终导致贯穿性优势剪切带形成,且剪切带的方向与Arthur理论更加符合.同时发现剪切带内外的颗粒体积分数和配位数等细观参数差异较大,结合J点对应的临界体积分数,可以判断在剪切带内部为unjammed体系,而外部为jammed体系,亦即沿剪切带界面发生了相变.

Granular matter is a large assemblage of dense packed particles. A granular skeleton frame is linked by grain-to-grain contacts. An external loading is usually transmitted through selective pathways from the skeleton frame,and heterogeneous force chain architecture is formed. The formation and evolution of shear band have importarit bearing to the stability of a granular assembly. In this work,the mechanical properties of granular matter under biaxial test are studied by using DEM simulations. Evolutions of stress,volumetric strain,coordination number,distribution of particle rotation and solid fractions are analyzed. The results show that within shear zone the solid fraction is smaller and the coordination number fluctuates violently,which indicates that they are unjammed,while beyond the shear band the particles are jammed. Therefore,we could say that the shear band actually corresponds to the complicated jamming transition. Three types of force chain configurations are observed under different axial strains： circle-shaped,column-shaped,both column and vortex-shaped. Such structures would be dominant to the mechanical properties of macro-mechanical properties and granular system,and pending further studies.