Understanding the mechanisms of amorphous creep through molecular simulation
Understanding the mechanisms of amorphous creep through molecular simulation
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DOI：
10.1073/pnas.1708618114
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发表时间：
2017-12-26
影响因子：
11.1
通讯作者：
Yip, Sidney
中科院分区：
文献类型：
--
作者：
Cao, Penghui;Short, Michael P.;Yip, Sidney
采用基于元胞力学的原子论方法，在实验时间尺度上模拟了金属玻璃薄膜中蠕变的分子过程。分析了原子应变和非仿射原子位移的时空演化，揭示了应力和热激活作用下非晶蠕变的原子级形变和流动过程.从模拟结果中，解决了空间上的纳米级和时间上的分数秒的时间增量，我们得到一个众所周知的蠕变速率与应力的变化的机械解释。我们还构建了一个变形图，描绘了在低应力和高温下的扩散蠕变和在高应力下的变形蠕变的主要制度。我们的研究结果验证了两个原始模型的非晶塑性机制的相关性：一个专注于原子扩散通过自由体积和其他专注于应力诱导的剪切变形。这些过程被发现是非线性耦合，通过动态异质波动的特点，系统的缓慢动态平衡。
Molecular processes of creep in metallic glass thin films are simulated at experimental timescales using a metadynamics-based atomistic method. Space-time evolutions of the atomic strains and nonaffine atom displacements are analyzed to reveal details of the atomic-level deformation and flow processes of amorphous creep in response to stress and thermal activations. From the simulation results, resolved spatially on the nanoscale and temporally over time increments of fractions of a second, we derive a mechanistic explanation of the well-known variation of creep rate with stress. We also construct a deformation map delineating the predominant regimes of diffusional creep at low stress and high temperature and deformational creep at high stress. Our findings validate the relevance of two original models of the mechanisms of amorphous plasticity: one focusing on atomic diffusion via free volume and the other focusing on stress-induced shear deformation. These processes are found to be nonlinearly coupled through dynamically heterogeneous fluctuations that characterize the slow dynamics of systems out of equilibrium.