Jin Weiwei, Datye Amit, Schwarz Udo D, Shattuck Mark D, O'Hern Corey S
Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06520, USA.
Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520, USA.
Soft Matter. 2021 Oct 6;17(38):8612-8623. doi: 10.1039/d1sm00898f.
We investigate the non-affine displacement fields that occur in two-dimensional Lennard-Jones models of metallic glasses subjected to athermal, quasistatic simple shear (AQS). During AQS, the shear stress strain displays continuous quasi-elastic segments punctuated by rapid drops in shear stress, which correspond to atomic rearrangement events. We capture all information concerning the atomic motion during the quasi-elastic segments and shear stress drops by performing Delaunay triangularizations and tracking the deformation gradient tensor associated with each triangle . To understand the spatio-temporal evolution of the displacement fields during shear stress drops, we calculate along minimal energy paths from the mechanically stable configuration immediately before to that after the stress drop. We find that quadrupolar displacement fields form and dissipate both during the quasi-elastic segments and shear stress drops. We then perform local perturbations (rotation, dilation, simple and pure shear) to single triangles and measure the resulting displacement fields. We find that local pure shear deformations of single triangles give rise to mostly quadrupolar displacement fields, and thus pure shear strain is the primary type of local strain that is activated by bulk, athermal quasistatic simple shear. Other local perturbations, rotations, dilations, and simple shear of single triangles, give rise to vortex-like and dipolar displacement fields that are not frequently activated by bulk AQS. These results provide fundamental insights into the non-affine atomic motion that occurs in driven, glassy materials.
我们研究了在二维金属玻璃的Lennard-Jones模型中，在无热、准静态简单剪切（AQS）作用下出现的非仿射位移场。在AQS过程中，剪应力-应变显示出连续的准弹性段，其间穿插着剪应力的快速下降，这对应于原子重排事件。我们通过执行德劳内三角剖分并跟踪与每个三角形相关的变形梯度张量，捕捉了准弹性段和剪应力下降期间原子运动的所有信息。为了理解剪应力下降期间位移场的时空演化，我们沿着从紧接应力下降之前的机械稳定构型到之后的机械稳定构型的最小能量路径进行计算。我们发现，四极位移场在准弹性段和剪应力下降期间都会形成和消散。然后，我们对单个三角形进行局部扰动（旋转、膨胀、简单剪切和纯剪切），并测量由此产生的位移场。我们发现，单个三角形的局部纯剪切变形主要产生四极位移场，因此纯剪切应变是由整体无热准静态简单剪切激活的主要局部应变类型。单个三角形的其他局部扰动，即旋转、膨胀和简单剪切，会产生涡旋状和偶极位移场，这些位移场在整体AQS中不常被激活。这些结果为驱动的玻璃态材料中发生的非仿射原子运动提供了基本见解。
