散粒介质剪切带细观力学结构几何演化与稳定性分析  

Geometry evolution and stability analysis for mesoscopic mechanical structure in shear band of granular media

作　　者：刘洋[1] 李爽 吴可嘉 LIU Yang;LI Shuang;WU Kejia(Department of Civil Engineering,, University of Science and Technology Beijing, Beijing 100083, China)

机构地区：[1]北京科技大学土木系,北京100083

出　　处：《岩石力学与工程学报》2018年第A01期3686-3700,共15页Chinese Journal of Rock Mechanics and Engineering

基　　金：国家自然科学基金资助项目(51178044);北京市优秀人才培养项目(2013D009006000005)~~

摘　　要：基于离散单元法对剪切带宏细观力学行为进行数值模拟,将通过网格剖分形成的loop单元作为细观力学的基本结构单元,对剪切带内、外不同类型loop单元的数量、几何形态、受力特征与抗滑稳定性的演化进行细致分析,讨论其发展变化与试样强度、剪胀发展之间的内在联系。模拟结果表明,剪切过程中剪切带内、外loop结构的数量和几何形态发展规律基本一致但强弱不同;其受力特征及抗滑稳定性在剪切带内、外产生了明显的差异。剪切过程中高阶loop单元比例增加且变得更扁平,低阶loop单元比例减少而形状基本保持不变。宏观尺度上的剪胀在细观力学结构演化上表现为低阶单元结构向高阶单元结构的转化,反映了试样在特定受力与边界条件下形成的自组织结构。提出2类滑动率的概念用于分析loop结构的抗滑稳定性,剪切带内、外滑动率在峰值后的发展趋势明显不同,最大滑动比例点与应力–应变关系曲线峰值应力点的相对位置也不同。剪切过程中高阶loop单元形成的强力链在力学层面上承担与传递了相对较大的外荷载,且抗滑稳定性较高;低阶loop单元抗滑稳定性差,其向高阶loop单元转化过程中发生的接触滑动与颗粒重组,是散体材料塑性变形发展的主要原因。The macro-and meso-mechanical behaviors of shear band were simulated using discrete element method. Loop structures were taken as the basic meso-mechanical unit of granular material after tessellation. The evolution of numbers,geometrical morphology,mechanical characteristic and sliding stabilities for different loops during shearing were analyzed in details,and the essential relationships were discussed between the variation of loops and the strength,dilatancy of granular material. Numerical results show that the variation of numbers and geometrical morphology of loop structures are approximately consistent inside and outside the shear band during shearing,but the degrees are different,the mechanical states and sliding stabilities of different loops inside and outside the shear band are obviously different. Proportions of higher-order loops are increasing and shapes of them are more flat,while proportions of lower-order loops are decreasing and shapes are keeping unchanged. The macro-scale dilatancy is reflected by the conversion from lower-order loops to higher-order loops in meso-scale mechanical structure,which forms a kind of self-organized structure under specific force and boundary condition. Two kinds of definition of sliding rate were proposed to analyze the sliding stabilities of loop structures. Evolution of sliding rate inside the shear band after peak stress state is obviously different from that outside the shear band,and the location of maximum sliding rate are not coincide with the location of peak stress point on stress-strain curve. The strong force chains,which are formed by higher-order loops,undertake larger load and have higher sliding stability than lower-order loops. The contact sliding and recombination during the conversion from lower-order loops to high-order loops are the main causes of plastic deformation for granular material.

关 键 词：数值模拟 散粒介质 剪切带 细观结构 剪胀 离散元法 

分 类 号：O241[理学—计算数学]