Shigeru Hamada

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.

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.