局部加卸载下立方体阵列接触力残留的细观特性

Mesoscopic characteristics of residual contact force in block array subjected to partial loading and unloading

基于光弹试验分析立方体阵列在一个分级加卸载周期下力链和颗粒位移的演化过程,结果表明,接触力和颗粒位移在卸载阶段均存在残留,且接触力和颗粒位移的演化特征一致表明,卸载过程中存在一个临界荷载值。通过建立主力链颗粒的串联接触模型,得出残留接触力取决于力链所受侧向摩阻力,包括颗粒间接触摩擦与咬合力。结合光弹条纹解析所得特征颗粒所受接触力,分析加卸载作用下主力链所受摩阻力的演化特征,得出加卸载过程中主力链所受摩阻力与外荷载呈正相关,表明随着外荷载的增大,颗粒体系的内摩擦作用逐渐发挥以抵抗外力;但相同外荷载下,加载和卸载阶段主力链所受摩阻力并不相等,是立方体阵列产生残留接触力的根源。

Photo-elastic test was performed to analyze the evolution of force chain and block displacement in block array under a multi-stage loading and unloading cycle. The results demonstrate that both the contact force and block displacement show the visible ‘hysteresis＇ during unloading. The evolution characteristics of both the contact force and block displacement indicate a critical load during unloading. A serial contact model was established to simplify the contact state of the block column transmitted by primary force chain,which reveals that the residual contact force depends on the lateral friction resistance,including the inter-particle friction and inter-particle lock. The contact force acted on the representative block was quantified by fringe analysis to achieve the evolution of lateral friction resistance on primary force chain during loading and unloading. The lateral friction resistance is positively associated with the applied load,indicating that greater inter-particle friction and contact resistance induced by the inter-particle lock are activated to resist the increasing applied load. The difference of lateral friction resistance under the same applied load between loading phase and unloading phase is the mechanism of residual contact force in block array.