Fracture simulations using large-scale molecular dynamics.
Fracture simulations using large-scale molecular dynamics.
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DOI：
10.1103/physrevb.51.11275
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发表时间：
1995-05
期刊：
影响因子：
--
通讯作者：
B. Holian;R. Ravelo
中科院分区：
文献类型：
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作者：
B. Holian;R. Ravelo
我们报告最近的分子动力学（MD）断裂模拟模式-I拉伸加载在高应变率。由于裂缝会发出声波，因此以前的模拟在超过一个声音穿越时间后变得不可靠。使用大规模并行MD，我们展示了如何消除不必要的边界效应和研究畅通的裂纹扩展机制。为了代表裂纹尖端附近的拉伸应力条件，我们采用单轴，均匀扩展的周期性边界条件，研究应变率，温度和相互作用潜力的影响。因为我们的样品足够大，我们看到位错以接近剪切波声速${\mathit{c}}_{\mathit{s}}$的速度从裂纹尖端发射出来。当它们移动许多晶格间距远离裂缝时，它们会减慢速度，最后以大约2/3${\mathit{c}}_{\mathit{s}}$的速度移动。每次位错发射时，裂纹尖端会出现“鱼尾”，在足够高的应变下，裂纹会分叉;位错会爬升并成为额外微裂纹的成核点。我们发现，我们可以通过在运动方程中包含粘性阻尼来抑制韧性行为，从而证明当接近静态、零应变率条件时，会向脆性裂纹传播转变。最后，我们表明，通过改变吸引尾的对潜力，我们可以改变一个韧性材料到脆性。在动态裂纹扩展下，延性和脆性行为之间的区别是模糊的：在脆性材料中，位错渐近地束缚在裂纹尖端，而在延性材料中，它们可以逃逸。
We report on recent molecular-dynamics (MD) fracture simulations of mode-I tensile loading at high strain rates. Because cracks emit sound waves, previous simulations became unreliable beyond one sound traversal time. Using massively parallel MD, we show how to eliminate unwanted boundary effects and study unimpeded crack propagation mechanisms. In order to represent tensile stress conditions near the crack tip, we employ uniaxial, homogeneously expanding periodic boundary conditions, examining the effects of strain rate, temperature, and interaction potential. Because our samples are sufficiently large, we see dislocations being emitted from the crack tip at nearly the shear-wave sound speed ${\mathit{c}}_{\mathit{s}}$. As they move many lattice spacings away from the crack, they slow down, finally moving at about 2/3${\mathit{c}}_{\mathit{s}}$. Each time dislocations are emitted, the crack tip ``fishtails,'' and at sufficiently high strain, the crack can fork; dislocations can climb and become nucleation sites for additional microcracks. We find that we can suppress ductile behavior by including viscous damping in the equations of motion, thereby demonstrating a transition to brittle crack propagation as static, zero-strain-rate conditions are approached. Finally, we show that, by altering only the attractive tail of the pair potential, we can change a ductile material into a brittle one. Under dynamic crack propagation, the distinction between ductile and brittle behavior is blurred: in brittle materials, dislocations are asymptotically bound to the crack tip, while in ductile materials, they can escape.