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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. [ABSTRACT FROM AUTHOR]

The appearance of strain localization (SL) in front of the crack tip is a factor that promotes transition toward the fatigue crack extension mode. Therefore, to predict fatigue crack extension behavior in case multiple modes occur, it is necessary to evaluate the degree of SL. In this study, the following simulations were performed on a single‐crystal twinning‐induced plasticity (TWIP) steel: (a) SL characterization by crystal plasticity finite element method (CPFEM) analysis of a smooth specimen under tension, (b) strain concentration (SC) characterization by EP‐FEM analysis of a cracked specimen under tension, and (c) characterization of interaction results between SC and SL of a cracked specimen under tension by CPFEM analysis. A comparison of the above results found that the interaction between SC and SL was large for long cracks and a significant strain field, different from the Hutchinson, Rice, Rosengren (HRR) singular field, was formed in front of the crack tip. Therefore, a parameter was proposed to quantify the SL properties in a smooth specimen. Subsequently, a fracture‐mechanics‐like method was proposed in which the results of (b) and the introduced parameters control the results of (c). Highlights: Crystal plasticity finite element model for crack with strain localization.Comparison between crystal plasticity and traditional finite element method.Strain localization affects the strain distribution around the crack tip.Strain localization changes the singularity at the crack tip. [ABSTRACT FROM AUTHOR]