Analytical Study on Effects of Microscopic Heterogeneity on Crack Generation in Ferrite/Martensite Dual-Phase Steels
Masahito MOCHIZUKI, Masaru KOHARA, Hiroshi SHIMANUKI, Yukito HAGIWARA and Masao TOYODA
Abstract:Numerical analysis is conducted in order to study the effects of microscopic heterogeneous morphology on crack generation in ferrite/martensite dual-phase steels. The macro-model of three-point bending specimen and the micro-model of heterogeneitic phases are connected with a boundary condition in the analysis. Stress distribution near fatigue precrack tip in the three-point bending specimen is calculated by the macro-model, and the stress-ratio of the triaxiality is used for the boundary condition of the micro-model. Microscopic unit cell is modeled by considering the strength heterogeneity between ferrite and martensite phases in a ferrite/martensite dual-phase steel. The relation between the characteristics of stress distribution and the heterogeneitic morphology are clarified from the numerical analysis, and the location of crack generation is investigated. The heterogeneitic morphology in the micro-model and CTOD in the macro-model are related by using the both results of the analytical models. The effects of the heterogeneitic morphology on crack generation are discussed. Key Words:Microscopic heterogeneity, Crack generation, Ferrite/martensite steel, Dual-phase steel, Elastic-plastic stress analysis, Macro-micro coupled analysis, Material design