加卸载状态下散粒体力链结构的复杂网络分析

Complex network analysis of force chain structure for granular materials underloading and unloading conditions

岩土类散粒体在加卸载过程中会呈现出不可逆的力学行为,可从复杂网络参数演化角度分析散粒体加卸载细观机制。采用离散单元法,进行散粒体加载―卸载―再加载过程的三轴数值模拟,并分析了加卸载过程中散粒体的宏观应力-应变演化及其对应的不同强接触体系的复杂网络特征。研究表明:散粒体的应力-应变曲线在加卸载过程中形成“滞回环”,在微观配位数和聚类系数上亦表现出了不可逆行为;采用不同阈值划分不同加卸载状态的强弱接触体系,随着阈值的增大,各应力状态对应的细观结构差异减小;强接触体系的最大簇在特定阈值区间内达到贯穿边界的极限,其几何特征与拓扑特征反映了散粒体加卸载过程的不可逆变化。

Granular materials are associated with the irreversible behaviors during the loading-unloading-reloading path,the mechanism of which can be analyzed in terms of complex network evolutions.In this paper,the discrete element method is used to conduct triaxial tests for granular materials under the loading-unloading-reloading condition.The macroscopic responses of the granular materials and its corresponding complex network characteristics of different strong contact systems are analyzed.It is found that the macroscopic“hysteresis loop”is formed during the loading-unloading-reloading path of dense granular materials,and the microscopic coordination numbers and clustering coefficients also exhibit irreversible behaviors.Different thresholds are used to classify the strong and weak contact systems for granular materials under different loading and unloading stress states,and the difference in the mesostructure corresponding to each stress state decrease as the threshold increases.The maximum cluster of the strong contact system reaches the limit of percolation when the force threshold falls in a range,and the irreversible behaviors of granular materials can be reflected in the geometric and topological features of strong network during the loading-unloadingreloading path.