Traditional fracture theories infer damage at cracks (local field) by surveying loading conditions away from cracks (far field). This approach has been successful in predicting ductile fracture, but it normally assumes isotropic and homogeneous materials. However, myriads of manufacturing procedures induce heterogeneous microstructural gradients that can affect the accuracy of traditional fracture models. This work presents a microstructure-sensitive finite element approach to explore the shielding effects of grain size and crystallographic orientation gradients on crack tip microplasticity and blunting. A dislocation density-based crystal plasticity model conveys texture evolution, grain size effects, and directional hardening by computing the constraint from dislocation structures. The results demonstrate that the microstructure can act as a buffer between the local and far fields that affects the crack tip microplasticity variability. For nominal opening loading, grain size and texture affect the local ductility and induce a non-negligible multiaxial plastic deformation. Furthermore, driving forces based on measuring displacements away from the crack tip are less affected by the microstructure, which suggests that traditional experimental methods smear out important crack tip variability.

中文翻译：

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微结构梯度介导的裂纹尖端微塑性

传统的断裂理论通过测量远离裂缝（远场）的载荷条件来推断裂缝（局部场）的损伤。这种方法在预测韧性断裂方面取得了成功，但它通常假设材料为各向同性和均质材料。然而，无数的制造过程会导致异质微观结构梯度，这会影响传统断裂模型的准确性。这项工作提出了一种微观结构敏感的有限元方法，以探索晶粒尺寸和晶体取向梯度对裂纹尖端微塑性和钝化的屏蔽效应。基于位错密度的晶体塑性模型通过计算位错结构的约束来传达织构演化、晶粒尺寸效应和定向硬化。结果表明，微观结构可以作为影响裂纹尖端微塑性变异性的局部场和远场之间的缓冲区。对于名义开口载荷，晶粒尺寸和纹理会影响局部延展性并引起不可忽略的多轴塑性变形。此外，基于测量远离裂纹尖端的位移的驱动力受微观结构的影响较小，这表明传统的实验方法抹去了重要的裂纹尖端变异性。