2014 年 100 巻 5 号 p. 668-677
The purpose of this study is to develop a simulation method to predict the effect of micro-structural characteristics of two-phase steel on two types of ductile properties related to ductile crack growth resistance of a structural component. One of the ductile properties is critical local strain related to shear-slip mode of ductile crack initiation, and another is stress triaxiality dependent ductility related to equi-axed dimple mode of ductile crack growth. A 3D mesoscopic damage simulation method that has been previously proposed by authors are utilized, where a 3D micro-structural FE-model having heterogeneous two phases along with a numerical damage model is applied. On the basis of the method, a small three-point bend specimen model with a deep notch is proposed to predict critical local strain. On the other hand, a method for predicting stress triaxiality dependent ductility is also proposed, where a representative volume element (RVE) loaded under constant stress triaxiality is applied. The two types of ductile properties for ferrite-pearlite two-phase steel predicted by the proposed methods present a good agreement with the experimental results. The developed simulation method can address the effect of micro-structural characteristics of two-phase steel to improve the ductile properties. Layered type morphology of a harder second phase is predicted to provide higher ductile properties than random type morphology as long as volume fraction of a second phase is the same.
