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arXiv 1502.01203cond-mat.soft
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二维非晶颗粒柱中的形变驱动扩散和塑性流动

Deformation-Driven Diffusion and Plastic Flow in Two-Dimensional Amorphous Granular Pillars

Wenbin Li, Jennifer M. Rieser, Andrea J. Liu, Douglas J. Durian, Ju Li

摘要:

我们报告了一个结合实验和模拟研究的变形引起的扩散在压实的二维非晶颗粒柱,其中热波动起着微不足道的作用。支柱,由直立在基板上的双分散圆柱形缩醛塑料颗粒组成,通过以恒定速度移动的刚性杆单轴和准静态地变形。柱中的塑性流动和颗粒重排的特征在于通过计算与两个变形阶段之间的每个颗粒相关联的最佳拟合仿射变换应变和非仿射位移。非仿射位移表现出指数交叉从弹道扩散行为的累积偏应变,表明在非热颗粒填料,累积偏应变在热系统中起着时间的作用,并驱动有效的颗粒扩散。通过数值模拟进一步研究了颗粒柱的尺寸效应,发现不同尺寸的颗粒柱在变形过程中遵循自相似的形状演化规律。此外,柱的屈服应力随柱尺寸线性增加。在变形过程中形成的瞬态剪切线的支柱变得更加明显的支柱尺寸的增加。这些基本剪切带的宽度约为颗粒直径的两倍,并且不随柱尺寸而变化。

英文摘要:

We report a combined experimental and simulation study of deformation-induced diffusion in compacted two-dimensional amorphous granular pillars, in which thermal fluctuations play negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and non-affine displacement associated with each particle between two stages of deformation. The non-affine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.

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