Deterministic approach on microstructurally small crack definition based on a crystalline plasticity finite element method incorporating strain localization

The transition point of the crack length to a microstructurally small crack is necessary for predicting crack extension behavior. The conventional criterion is the crack length smaller than the grain size and is a probabilistic criterion. This criterion does not consider the metal's crystallite plasticity property discrepancy (CPPD). However, CPPD determines crack extension behavior for recently developed advanced materials with complex microstructures. Therefore, the authors propose a deterministic judgment method for microstructurally small cracks considering crystallite plasticity based on a physics-based crystal plasticity finite element model with strain localization. The proposed method is based on the difference value of the crack tip opening displacement varying with the ratio between the crack length and grain size with the change in the grain orientation ahead of the crack tip. A case study for copper is performed, and the results show that the novel method can be applied to define the microstructurally small crack.