局部加卸载下散粒体中接触力的残留特性及细观机理

Residual Characteristics and Meso Mechanism of Contact Force in Granular Materials Under Partial Loading and Unloading

摘要:

基于光弹试验分析了正五棱柱颗粒体系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，强力链上的接触力和颗粒位移在卸载释放时均存在“残留”现象，卸载阶段颗粒位移正响应区域大于加载阶段.定义量纲一化的位移恢复率ηd(-1<ηd<1)描述颗粒运动轨迹，并给出颗粒运动的五种类型所对应的ηd取值；随着深度的增大，ηd逐渐增大.力链和颗粒位移的演化特性表明，存在一个临界荷载值，当附加荷载高于临界值时，散粒体内残留接触力处于稳定平衡状态；当卸载至临界值时，残留接触力达到极限平衡状态，进一步卸载残留接触力将快速释放，并引起颗粒位置重分布.

关键词:散粒体; 局部加卸载; 残留接触力; 颗粒位移; 光弹试验

Abstract:

A photoelastic experiment was conducted to analyze the evolution characteristics of force chain network and granule displacement in pentagons under a complete loading and unloading cycle. The results demonstrate that both contact force within the strong force chain and granule displacement show a visible “hysteresis” phenomenon during unloading; the area where granule displacement response is positive during unloading is larger than the area during loading. The displacement recovery ratio ηd((1<ηd<1) was defined to describe the movement locus of granules. Then the relationship between ηd and five types of movement locus were built. ηd increases along the depth. Evolution characteristics of both force chain and granule displacement show a critical level of superload. The residual contact force in granular material is at the state of stable equilibrium when superload is higher than the critical level while reaches the limit equilibrium state when unloading to the critical level. Further unloading will result in instant release of residual contact force as well as the redistribution of granules.

Key words:granular material; partial loading and unloading; residual contact force; granule displacement; photoelastic experiment