組織不均質を考慮した三次元延性損傷シミュレーション法: 複相組織材料の延性予測

摘要

近年の高靭性材料の開発により，延性き裂の進展を伴う場合の構造性能評価の重要性が益々増してきている。そのため，延性き裂の進展抵抗を定量的に予測する技術の確立が期待される。これまで，構造部材の延性き裂進展抵抗を予測する手法について精力的に検討されており，材料の損傷挙動をモデル化（数式化）して数値シミュレーションにより直接予測する方法が各種提案されている。%The effort of this study is to establish simulation method for predicting the effect of mechanical and morphological characteristics of each constituent phase of two-phase steel on two types of ductile properties that has been found to be ductile crack growth resistance controlling mechanical properties; one is critical local strain that controls shear mode ductile cracking, and the other is stress triaxiality dependent ductility. Notched micro-tensile tests for ferrite-pearlite two-phase steel exhibits that ductile failures from specimen center with dimple mode and notch-root surface with shear mode are both controlled by micro-void nucleation at softer ferrite phase near ferrite/pearlite boundary. 3D micro-structural FE-model is developed for analyzing the stress/strain localization behaviors associated with heterogeneous microstructure in strength, and ductile damage model for reproducing damage evolution up to micro-void/micro-crack formation is proposed. The 3D meso-scopic damage simulation method is applied for simulating ductile cracking behaviors of notched tensile specimens of two-phase steel. The damage evolution associated with micro-structural heterogeneity up to ductile cracking from specimen center as well as notch-root surface is well predicted.