形变金属玻璃中剪切带形成的软局域畴引发
The Initiation of Shear Band Formation in Deformed Metallic Glasses from Soft Localized Domains
摘要：
长期以来，人们一直认为非晶态固体中剪切带（SB）的形成始于材料中的相对“软”区域，在该区域中大尺度非仿射变形变得局部化。这个假设的测试需要一个有效的方法来识别“软”区域及其演变，因为材料变形到不同程度，其中“柔软度”的度量还必须考虑温度对局部材料刚度的影响。我们表明，均方原子位移上的一个笼子里的时间尺度<u2>，“德拜-沃勒因子”，提供了一个有用的方法来估计整个材料的剪切模量，并通过扩展，在原子尺度上的材料刚度。基于这种“软”度量，我们观察到，SB的形成确实发生通过应变诱导形成的局部软区域在我们变形的金属玻璃自支撑膜。出乎意料的是，SB形成的临界应变条件发生时，<u2>出现的软区域内的柔软度（）分布接近界面区域在其未变形状态，开始不稳定性与过渡到湍流的相似。相应地，当材料如此薄以至于整个材料可以近似地描述为本质上是“界面”时，不会出现SB。我们还量化的玻璃和高度非高斯粒子位移的性质和起源的动态异质SB区域的时间比笼子里的时间更长的放松。
英文摘要：
It has long been thought that shear band (SB) formation in amorphous solids initiates from relatively 'soft' regions in the material in which large-scale non-affine deformations become localized. The test of this hypothesis requires an effective means of identifying 'soft' regions and their evolution as the material is deformed to varying degrees, where the metric of 'softness' must also account for the effect of temperature on local material stiffness. We show that the mean square atomic displacement on a caging timescale <u2>, the 'Debye-Waller factor', provides a useful method for estimating the shear modulus of the entire material and, by extension, the material stiffness at an atomic scale. Based on this 'softness' metrology, we observe that SB formation indeed occurs through the strain-induced formation of localized soft regions in our deformed metallic glass free-standing films. Unexpectedly, the critical strain condition of SB formation occurs when the softness (<u2>) distribution within the emerging soft regions approaches that of the interfacial region in its undeformed state, initiating an instability with similarities to the transition to turbulence. Correspondingly, no SBs arise when the material is so thin that the entire material can be approximately described as being 'interfacial' in nature. We also quantify relaxation in the glass and the nature and origin of highly non-Gaussian particle displacements in the dynamically heterogeneous SB regions at times longer than the caging time.
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