弹塑性颗粒物质准静态变形的细观力学行为

Micromechanics of granular assemblies of elastic-perfectly plastic spheres during quasi-static deformation

本文介绍了对由弹塑性圆球组成的粒度多分散系统进行的轴向准静态加载和卸载的数值模拟成果。首先介绍了基于理论接触力学导出的颗粒弹塑性接触模型,进而阐明了基于颗粒离散元法对颗粒物质准静态变形模拟的基本方法。研究发现:弹塑性球颗粒系统在加载时其轴向刚度对颗粒间产生的塑性变形量及颗粒间的摩擦均很敏感。然而,颗粒间的摩擦对轴向加载时系统产生的水平应力没有很强的影响。数值模拟还提供了颗粒量级上的微力学内部变量的信息。这里引入并介绍了结构异性张量、滑动接触比率以及平均配位数。通过对这些参数的研究表明:在卸载的全过程中,颗粒间相对滑移出现,相互作用的颗粒数减少,系统内部结构产生不可恢复变形。因此,尽管在卸载应力应变曲线的初始段约为线性,但这并不意味着颗粒系统的响应如传统连续力学中假定的那样为弹性。

Quasi-static deformation of granular materials was examined by performing discrete element simulations on polydisperse systems of elastic-perfectly plastic spheres in a periodic cell. Results of simulations of unaxial compression and decompression tests were reported for a 3D system of elastic-perfectly plastic spheres. Based on the theoretical contact mechanics, the numerical simulations demonstrated that the axial stiffness during compression was sensitive to both the amount of plastic deformation and the interparticle friction occurring at the contacts within the assembly of particles. However, the interparticle friction did not appear to have a significant effect on the magnitude of the lateral stress developed during the uniaxial compression. Discrete element simulation also permitted a detailed examination of the evolution of internal variables associated with the micromechanical processes occurring at the particle scale. In this context, the evolution of the induced structural anisotropy, the percentage of sliding contacts, and the average coordination number were presented and discussed. It was shown that at all stages of unloading, interparticle sliding occurred, the number of interparticle contacts reduced and irrecoverable deformation of the microstructure occurred. Consequently, although the initial part of the unloading stress-strain curve might be approximately linear, this did not mean that the system response was elastic, as frequently assumed in continuum theories.