The plastic events occurring during the process of intergranular fracture in metals is still not well understood due to the complexity of grain boundary (GB) structures and their interactions with crack-tip dislocation plasticity. By considering the local GB structural transformation after dislocation emission from a GB in the Peierls-type Rice-Beltz model, herein we established a semi-analytical transition-state-theory-based framework to predict the most probable Mode-I stress intensity factor (SIF) for dislocation emission from a cracked GB. Using large-scale molecular dynamics (MD) simulations, we studied the fracture behaviors of bi-crystalline Fe samples with 12 different symmetric tilt GBs inside. The MD results demonstrate that the presence of GB could significantly change the SIF required for the activation of plastic events, confirming the theoretical predictions that attributes this to the energy change caused by the transformation of GB structure. Both the atomistic simulation and the theoretical model consistently indicate that, the critical dynamic SIF (KIc(t)) at which the dynamic SIF KI(t) deviates from the linearity with respect to the strain ε, increases with the increasing loading rate. However, the classical Rice model underestimates the KIc(t) due to its failure to consider the effects of localized fields. The present theoretical model provides a mechanism-based framework for the application of grain boundary engineering in the design and fabrication of nano-grained metals.

中文翻译：

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晶间断裂的扩展 Rice 模型


由于晶界 （GB） 结构的复杂性及其与裂纹尖端位错塑性的相互作用，金属晶间断裂过程中发生的塑性事件仍未得到很好的理解。通过在 Peierls 型 Rice-Beltz 模型中考虑 GB 位错发射后的局部 GB 结构转变，我们建立了一个基于半分析过渡状态理论的框架来预测裂纹 GB 位错发射的最可能的 I 型应力强度因子 （SIF）。使用大规模分子动力学 （MD） 模拟，我们研究了内部有 12 个不同对称倾斜 GB 的双晶 Fe 样品的断裂行为。MD 结果表明，GB 的存在可以显着改变塑性事件激活所需的 SIF，证实了将其归因于 GB 结构转变引起的能量变化的理论预测。原子模拟和理论模型一致表明，动态 SIF KI（t） 偏离相对于应变ε线性度的临界动态 SIF （KIc（t）） 随着加载速率的增加而增加。然而，经典的 Rice 模型低估了 KIc（t），因为它没有考虑局部场的影响。该理论模型为晶界工程在纳米晶粒金属设计和制造中的应用提供了一个基于机制的框架。