循环扭转剪切下圆筒内硬球颗粒的致密化行为

Compaction behaviors of hard spherical granules in cylinder subject to cyclic torsional shear

基于圆筒内硬球颗粒的致密化过程涉及应力传递与堆积结构的耦合作用,是颗粒介质研究中的一个难点问题,为此,采用MTS 858 Mini Bionix Ⅱ型力学性能测试仪,通过改变压力、颗粒粒径、剪切速率等参数,对循环扭转剪切作用下的致密化行为进行实验研究。研究结果表明:颗粒介质致密化过程表现为快速致密和缓慢致密2个阶段,体积分数的演化过程满足双指数项关联函数,即φ(t)=φ0+A1(1-exp(-t/t1))+A2(1-exp(-t/t2))(其中,φ0为系统初始体积分数,A1和A2为拟合系数,t1和t2分别为快速和缓慢致密过程的特征时间);系统经历快速堵塞过程后,进入颗粒缓慢重排过程;在循环剪切过程中,颗粒体积分数的涨幅Δφ在体积分数达到0.604时发生由降转升的转变;增大压力、粒径与圆筒直径之比(d/D)以及剪切速率均有利于提高致密化程度,循环扭转剪切作用比纯剪切和垂直振动作用的致密化效率更高。

Considering that the coupling of stress transmission and structural organization during the compaction process of hard spheres in a cylinder is difficult to be described, a series of experiments were carried out to study this process, using the MTS 858 Mini Bionix Ⅱ type mechanical property tester. The compaction was studied as a function of confining pressure, particle size and shear rate. The results show that the compaction process is characterized by two time scales, i.e. t1 and t2, volume fraction satisfies φ( t )=φ0 + A1 ( 1-exp (-t/t1))+ A2 ( 1-exp (-t/t2)), where φ0 is the initial volume fraction, A1 and A2 are fitted coefficients. t1 and t2 are characteristic time of rapid and slow compaction process, respectively. After the system goes through the state of rapid compaction, it enters a creep regime involving slow rearrangement of particles. The increase of the volume fraction Δφ undergoes a transition from decrease to increase when the volume fraction reaches 0.604. The rate of compaction and the final volume fraction increase with the increase of the pressure, the ratio of sphere size to cylinder diameter(d/D) and shear rate. Compaction is more efficient subject to cyclic torsional shear than that pure shear and vertical vibration.