Abstract
AbstractTraditional 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.
Highlights
Ductile failure in metals is an intrinsic multiscale problem: forces applied far from a crack translate into crack blunting, growth, and failure, which are controlled by atom decohesion and defect aggregation
We present the results from microstructuresensitive models, isotropic elastic models, and isotropic elasto-plastic models constructed with the piece-wise stress-strain curve in Figure 3 and von Mises yield surface criteria.[51]
These results demonstrate that under displacement control, the ΔCMOD is insensitive to the microstructure while ΔCTOD and ΔδA can be affected by the microstructure
Summary
Ductile failure in metals is an intrinsic multiscale problem: forces applied far from a crack translate into crack blunting, growth, and failure, which are controlled by atom decohesion and defect aggregation (e.g., dislocations and vacancies). Microstructural attributes such as grain morphology, lattice orientation, material phases, and heterogeneous defect densities regulate the fracture driving force at the crack tip. Fracture mechanics driving forces—e.g., crack tip opening displacement (CTOD), stress intensity factor (K), and J-integral1—depend on the microstructure in between the local and the far field. Traditional fracture approaches assume homogeneous and isotropic materials with self-similar crack tip stress and strain fields,[2] which may not be representative of heterogeneous materials. The J-integral becomes path-dependent[3,4] for a crack growing towards an interface (Figure 1) with different material properties (e.g., welded material or a grain boundary). The J-integral in the neighborhood of the crack tip (Jtip)[5] may still
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