Delft University of Technology, Process & Energy Laboratory, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.
Soft Matter. 2017 Oct 4;13(38):6870-6876. doi: 10.1039/c7sm01700f.
We report the results of molecular dynamics simulations of stress relaxation tests in athermal viscous soft sphere packings close to their unjamming transition. By systematically and simultaneously varying both the amplitude of the applied strain step and the pressure of the initial condition, we access both linear and nonlinear response regimes and control the distance to jamming. Stress relaxation in viscoelastic solids is characterized by a relaxation time τ* that separates short time scales, where viscous loss is substantial, from long time scales, where elastic storage dominates and the response is essentially quasistatic. We identify two distinct plateaus in the strain dependence of the relaxation time, one each in the linear and nonlinear regimes. The height of both plateaus scales as an inverse power law with the distance to jamming. By probing the time evolution of particle velocities during relaxation, we further identify a correlation between mechanical relaxation in the bulk and the degree of non-affinity in the particle velocities on the micro scale.
我们报告了在接近无定形转变的无热粘性软球堆积体中进行应力松弛测试的分子动力学模拟结果。通过系统地同时改变施加应变步的幅度和初始条件的压力，我们可以访问线性和非线性响应区域，并控制与阻塞的距离。粘弹性固体中的应力松弛的特征是弛豫时间 τ*，它将粘性损失较大的短时间尺度与弹性储存为主、响应基本上是准静态的长时间尺度分开。我们在弛豫时间与应变的关系中确定了两个明显的平台，一个在线性区，一个在非线性区。两个平台的高度都与与阻塞的距离呈反比幂律关系。通过探测弛豫过程中颗粒速度的时间演化，我们进一步在颗粒速度的微观非关联程度和整体力学弛豫之间发现了一种相关性。
