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).

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Our previous study demonstrated that, in a cracked single‐crystal subjected to remote tensile stress, the interactions among material behavior, strain localization, mechanical behavior, and strain concentration caused the formation of a strain field was quite different from the HRR singularity introduced in the homogeneous continuum. Moreover, to quantify strain localization ability for metals, a material index for strain localization susceptibility (SLS) was proposed. However, the effectiveness and availability of that index were not examined in detail. In this study, a Cu‐based single crystal was examined using the crystal‐plasticity finite element method (CPFEM) model. This model incorporates the strain localization mechanism from the non‐crystallographic shear band. Additionally, a new material index for SLS was introduced. The results showed that the new material index could reflect the SLS of the material. Meanwhile, a critical material index value based on strain localization was determined for predicting the crack behavior. This study also discusses the plastic deformation behavior near the crack tip with different material indices for SLS.

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