Center for Complexity and Biosystems, Department of Physics, University of Milan, via Celoria 16, 20133 Milano, Italy.
Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
Phys Rev E. 2019 Dec;100(6-1):060602. doi: 10.1103/PhysRevE.100.060602.
Plastic instabilities in amorphous materials are often studied using idealized models of binary mixtures that do not capture accurately molecular interactions and bonding present in real glasses. Here we study atomic-scale plastic instabilities in a three-dimensional molecular dynamics model of silica glass under quasistatic shear. We identify two distinct types of elementary plastic events, one is a standard quasilocalized atomic rearrangement while the second is a bond-breaking event that is absent in simplified models of fragile glass formers. Our results show that both plastic events can be predicted by a drop of the lowest nonzero eigenvalue of the Hessian matrix that vanishes at a critical strain. Remarkably, we find very high correlation between the associated eigenvectors and the nonaffine displacement fields accompanying the bond-breaking event, predicting the locus of structural failure. Both eigenvectors and nonaffine displacement fields display an Eshelby-like quadrupolar structure for both failure modes, rearrangement, and bond breaking. Our results thus clarify the nature of atomic-scale plastic instabilities in silica glasses, providing useful information for the development of mesoscale models of amorphous plasticity.
非晶态材料中的塑性失稳通常使用二元混合物的理想化模型进行研究，这些模型不能准确捕捉真实玻璃中存在的分子相互作用和键合。在这里，我们在二氧化硅玻璃的三维分子动力学模型中研究了准静态剪切下的原子尺度塑性失稳。我们确定了两种不同类型的基本塑性事件，一种是标准的准局部原子重排，而另一种是在脆弱玻璃形成体的简化模型中不存在的键断裂事件。我们的结果表明，这两种塑性事件都可以通过 Hessian 矩阵的最低非零特征值的下降来预测，该值在临界应变处为零。值得注意的是，我们发现与键断裂事件伴随的关联特征向量和非仿射位移场之间存在非常高的相关性，从而预测了结构失效的位置。对于两种失效模式，即重排和键断裂，特征向量和非仿射位移场都显示出类似 Eshelby 的四极结构。因此，我们的结果澄清了二氧化硅玻璃中原子尺度塑性失稳的性质，为非晶态塑性的介观模型的发展提供了有用的信息。
