Institute for Complex Materials, IFW Dresden , Helmholtzstraße 20, D-01069 Dresden, Germany.
Institute of Materials Science, Technische Universität Darmstadt , Otto-Berndt-Strasse 3, D-64287 Darmstadt, Germany.
Nano Lett. 2018 Feb 14;18(2):1221-1227. doi: 10.1021/acs.nanolett.7b04816. Epub 2018 Jan 27.
Because of the fast dynamics of shear band formation and propagation along with the small size and transient character of the shear transformation zones (STZs), the elementary units of plasticity in metallic glasses, the description of the nanoscale mechanism of shear banding often relies on molecular dynamics (MD) simulations. However, the unrealistic parameters used in the simulations related to time constraints may raise questions about whether quantitative comparison between results from experimental and computational analyses is possible. Here, we have experimentally analyzed the strain field arising across an individual shear band by nanobeam X-ray diffraction and compared the results with the strain characterizing a shear band generated by MD simulations. Despite their largely different spatiotemporal scales, the characteristic features of real and simulated shear bands are strikingly similar: the magnitude of the strain across the shear band is discontinuous in both cases and the direction of the principal strain axes exhibits the same antisymmetric profile. This behavior can be explained by considering the mechanism of STZ activation and percolation at the nanoscale, indicating that the nanoscale effects of shear banding are not limited to the area within the band but they extend well into the surrounding elastic matrix. These findings not only demonstrate the reliability of MD simulations for explaining (also quantitatively) experimental observations of shear banding but also suggest that designed experiments can be used the other way around to verify numerical predictions of the atomic rearrangements occurring within a band.
由于剪切带的形成和传播具有快速动力学特性，以及剪切变形区（STZ）的尺寸小且具有瞬态特性，这些 STZ 是金属玻璃中塑性的基本单元，因此，对剪切带形成的纳米尺度机制的描述通常依赖于分子动力学（MD）模拟。然而，由于时间限制而在模拟中使用的不现实参数可能会引发这样的问题，即实验和计算分析结果之间是否可以进行定量比较。在这里，我们通过纳米束 X 射线衍射实验分析了单个剪切带中产生的应变场，并将结果与通过 MD 模拟生成的剪切带的应变特征进行了比较。尽管它们具有很大的时空尺度差异，但真实和模拟剪切带的特征非常相似：在两种情况下，剪切带的应变幅度都是不连续的，主应变轴的方向呈现相同的反对称分布。这种行为可以通过考虑 STZ 在纳米尺度上的激活和渗流机制来解释，表明剪切带形成的纳米尺度效应不仅限于带内区域，而且延伸到周围的弹性基质中。这些发现不仅证明了 MD 模拟对于解释（也定量地）剪切带形成的实验观察结果的可靠性，而且还表明，可以反过来设计实验来验证带内原子重排的数值预测。
