Low-speed fracture instabilities in a brittle crystal
Low-speed fracture instabilities in a brittle crystal
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DOI：
10.1038/nature07297
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发表时间：
2008-10-30
期刊：
影响因子：
64.8
通讯作者：
De Vita, A.
中科院分区：
文献类型：
--
作者：
Kermode, J. R.;Albaret, T.;De Vita, A.
当脆性材料加载到其强度极限时，它会由于裂纹的形核和扩展而失效(1)。裂纹扩展的条件是由裂纹尖端区域的应力集中造成的，并取决于宏观参数，如试件的几何形状和尺寸(2)。然而，裂纹的扩展方式完全由原子尺度现象决定，因为脆性的裂纹尖端在原子上是尖锐的，通过在移动的裂纹前沿的每个点(1，3)一次一个地破坏不同方向的原子间键来扩展。多种长度尺度的物理相互作用使脆性断裂成为一种复杂的“多尺度”现象。在更复杂的情况下，例如在存在微缺陷或晶界的情况下，可能会出现几个中间尺度。在超高速下裂纹扩展中出现的各种不稳定性是众所周知的(1)，最近在理解它们的起源方面取得了重大进展(4，5)。在这里，我们使用量子力学混合、多尺度模型和单晶断裂实验来研究硅中的低速传播不稳定性。我们的模拟预测了裂纹尖端的重建，这将使低速裂纹在(111)解理面上不稳定地扩展，而解理面通常被认为是最稳定的解理面。我们使用一种为研究低拉伸载荷下的断裂而设计的实验技术，在低速范围内观察到这种不稳定性。进一步的模拟解释了为什么在中高速下，裂纹在(110)解理面上的扩展变得不稳定并偏转到(111)面上，正如先前实验所观察到的(6，7)。
When a brittle material is loaded to the limit of its strength, it fails by the nucleation and propagation of a crack(1). The conditions for crack propagation are created by stress concentration in the region of the crack tip and depend on macroscopic parameters such as the geometry and dimensions of the specimen(2). The way the crack propagates, however, is entirely determined by atomic- scale phenomena, because brittle crack tips are atomically sharp and propagate by breaking the variously oriented interatomic bonds, one at a time, at each point of the moving crack front(1,3). The physical interplay of multiple length scales makes brittle fracture a complex 'multi-scale' phenomenon. Several intermediate scales may arise in more complex situations, for example in the presence of microdefects or grain boundaries. The occurrence of various instabilities in crack propagation at very high speeds is well known(1), and significant advances have been made recently in understanding their origin(4,5). Here we investigate low- speed propagation instabilities in silicon using quantum- mechanical hybrid, multi- scale modelling and single- crystal fracture experiments. Our simulations predict a crack- tip reconstruction that makes low- speed crack propagation unstable on the ( 111) cleavage plane, which is conventionally thought of as the most stable cleavage plane. We perform experiments in which this instability is observed at a range of low speeds, using an experimental technique designed for the investigation of fracture under low tensile loads. Further simulations explain why, conversely, at moderately high speeds crack propagation on the ( 110) cleavage plane becomes unstable and deflects onto ( 111) planes, as previously observed experimentally(6,7).