Potential energy landscape activations governing plastic flows in glass rheology
Potential energy landscape activations governing plastic flows in glass rheology
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DOI：
10.1073/pnas.1907317116
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发表时间：
2019-09-17
影响因子：
11.1
通讯作者：
Yip, Sidney
中科院分区：
文献类型：
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作者：
Cao, Penghui;Short, Michael P.;Yip, Sidney
虽然玻璃在天然和人造材料中无处不在，但控制其变形的原子水平机制以及这些机制与流变行为的关系仍然是基本理解的开放问题。通过在施加应变速率上跨越近10个数量级的原子模拟，我们探索了与均匀和非均匀剪切流的3种特征机制相关的原子重排。在低应变率和高应变率极限下，模拟结果和理论模型显示流动应力随应变率变化具有明显的标度行为，表明热激活扩散与应力驱动运动之间存在非线性耦合。此外，我们发现流动非均质性的出现与局部应变爆发的极值密切相关，这些极值不容易被周围环境所适应，作为剪切局部化的起源。通过分析非仿射粒子位移的距离矩阵来解释流态的原子机制，得到了分形势能景观（PEL）上各种障碍跳跃过程的证据，其中剪切转化和液体状区域是由热和应力激活的相互作用触发的。
While glasses are ubiquitous in natural and manufactured materials, the atomic-level mechanisms governing their deformation and how these mechanisms relate to rheological behavior are still open questions for fundamental understanding. Using atomistic simulations spanning nearly 10 orders of magnitude in the applied strain rate we probe the atomic rearrangements associated with 3 characteristic regimes of homogeneous and heterogeneous shear flow. In the low and high strain-rate limits, simulation results together with theoretical models reveal distinct scaling behavior in flow stress variation with strain rate, signifying a nonlinear coupling between thermally activated diffusion and stress-driven motion. Moreover, we find the emergence of flow heterogeneity is closely correlated with extreme values of local strain bursts that are not readily accommodated by immediate surroundings, acting as origins of shear localization. The atomistic mechanisms underlying the flow regimes are interpreted by analyzing a distance matrix of nonaffine particle displacements, yielding evidence of various barrier-hopping processes on a fractal potential energy landscape (PEL) in which shear transformations and liquid-like regions are triggered by the interplay of thermal and stress activations.