粒料固有各向异性的离散元模拟与细观分析

料在摊铺后形成的颗粒定向排列将导致其力学性质的固有各向异性. 依据粒料的实际不规则形状, 构建了可模拟粒间咬合嵌挤作用的三维离散元复杂形状颗粒; 生成了5 种不同沉积方向的各向异性试件和1种各向同性试件, 对比了各试件在三轴压缩试验中的宏观力学特性差异; 引入组构张量以量化各向异性程度, 利用玫瑰图表达接触法向与接触力的分布特征, 探究了粒料各向异性的细观发展规律. 结果表明: 颗粒长轴愈趋向水平排布, 峰值应力比愈大, 剪缩与剪胀程度愈明显; 相较于各向同性试件, 沉积角$\theta$为料在摊铺后形成的颗粒定向排列将导致其力学性质的固有各向异性. 依据粒料的实际不规则形状, 构建了可模拟粒间咬合嵌挤作用的三维离散元复杂形状颗粒; 生成了5 种不同沉积方向的各向异性试件和1种各向同性试件, 对比了各试件在三轴压缩试验中的宏观力学特性差异; 引入组构张量以量化各向异性程度, 利用玫瑰图表达接触法向与接触力的分布特征, 探究了粒料各向异性的细观发展规律. 结果表明: 颗粒长轴愈趋向水平排布, 峰值应力比愈大, 剪缩与剪胀程度愈明显; 相较于各向同性试件, 沉积角$\theta$为$0^\circ$时, 峰值应力比和最大体积压缩应变分别提高了12.6\%和18.8\%, 其原因在于加载过程中颗粒旋转和滑动百分比更小, 内部调整时间更短、更易被剪密; 固有各向异性对颗粒法向接触力分布的影响不大, 但显著影响接触法向分布特征; 剪切过程中, $\theta$为$90^\circ$时的接触法向各向异性系数先快速减小后逐渐增大, 而$\theta$为$0^\circ$到$60^\circ$时则呈现出增大后稍有回落或趋于稳定的趋势, 且$\theta$ 愈小的试件各向异性系数增大愈快.

SIMULATION AND MICRO-MECHANICS ANALYSIS OF INHERENT ANISOTROPY OF GRANULAR BY DISTINCT ELEMENT METHOD1)

The particles tend to be spatially arranged in directional orientation after the paving of granular materials, and thus leading to the inherent anisotropy of mechanical property. Based on the actual irregular shape of granular materials, three-dimensional complex shape particles were modelled utilizing distinct element method to simulate the interlocking between particles. Five numerical test specimens with different bedding angles and an isotropic specimen were established respectively, and the mechanical properties of various specimens were compared during the triaxial compression simulations. Besides, the fabric tensor was introduced to quantify the anisotropy, the rose diagram was drawn to exhibit the distribution characteristics of contact normal and contact force, and then the development of anisotropy was investigated. It is shown that, as the long axis of particles change toward the horizontal direction, the stress ratio and the shear dilatancy of specimen increase continuously. Compared with isotropic structure, the peak stress ratio and the maximal volume compression strain of anisotropic structure when the bedding angle $\theta=0^\circ$ is 12.6% and 18.8% larger respectively. This is because the rotation and contact sliding ratio of particles is smaller, the internal adjustment time is shorter, and specimen can be sheared more densely. The inherent anisotropy has little effect on the distribution characteristics of contact force, but significantly affects the distribution characteristics of contact normal. When $\theta$ is $90^\circ$, the contact normal anisotropy coefficient drops quickly and then gradually increases during the shear process. Otherwise, the coefficient shows a steady or slight drop trend after an increase, and the coefficient grows faster as the $\theta$ decreases.