Structural relaxation affecting shear-transformation avalanches in metallic glasses
Structural relaxation affecting shear-transformation avalanches in metallic glasses
复制标题
DOI：
10.1103/physreve.100.043002
复制
发表时间：
2019-10-02
影响因子：
2.4
通讯作者：
Ogata, Shigenobu
中科院分区：
文献类型：
--
作者：
Niiyama, Tomoaki;Wakeda, Masato;Ogata, Shigenobu
雪崩行为以幂律统计和结构松弛为特征，在非晶塑性中引起剪切局部化，在决定非晶金属固体（即金属玻璃）的力学性能中起着至关重要的作用。然而，它们之间的相互依赖仍然没有被完全理解。为了研究结构松弛对基本雪崩行为的影响，我们使用两种典型的金属玻璃模型对金属玻璃的剪切变形试验进行了分子动力学模拟，这两种典型的金属玻璃模型分别包括较不松弛（淬火）玻璃和较松弛（良好老化）玻璃，分别表现出相对均匀的变形和剪切带状的非均匀变形。两种玻璃模型的初等雪崩数据遵循相同的幂律统计，但最大事件大小不同，松弛良好的玻璃表现出剪切局部化。通过对每次基本雪崩事件中原子非仿射平方位移的空间相关函数的计算，我们观察到，在弛豫良好的玻璃中，基本雪崩区域的形状倾向于各向异性，而在弛豫较差的玻璃中，基本雪崩区域的形状则相对各向同性。此外，我们证明了雪崩传播方向上的时间聚类，并且在良好松弛的玻璃模型中，各向异性与雪崩大小之间存在相当大的相关性。
Avalanche behaviors, characterized by power-law statistics and structural relaxation that induces shear localization in amorphous plasticity, play an essential role in deciding the mechanical properties of amorphous metallic solids (i.e., metallic glasses). However, their interdependence is still not fully understood. To investigate the influence of structural relaxation on elementary avalanche behavior, we perform molecular-dynamics simulations for the shear deformation test of metallic glasses using two typical metallic-glass models comprising a less-relaxed (as-quenched) glass and a well-relaxed (well-aged) glass exhibiting a relatively homogeneous deformation and a shear-band-like heterogeneous deformation, respectively. The data on elementary avalanches obtained from both glass models follow the same power-law statistics with different maximum event sizes, and the well-relaxed glass shows shear localization. Evaluating the spatial correlation functions of the nonaffine squared displacements of atoms during each elementary avalanche event, we observe that the shapes of the elementary avalanche regions in the well-relaxed glasses tend to be anisotropic, whereas those in the less-relaxed glasses are relatively isotropic. Furthermore, we demonstrate that a temporal clustering in the direction of the avalanche propagation emerges, and a considerable correlation between the anisotropy and avalanche size exists in the well-relaxed glass model.