Three-dimensional modeling to compute plastic zone in front of crack in compact tension sample of multiphase material

Abstract

Two-dimensional modeling to compute plastic zone in front of a crack in a compact tension specimen of a multiphase material was published previously. This paper is the continuation of it, using the same concept, but in three dimensions. The heart of this study is to develop a simulation method to predict the effect of microstructural morphology in multiphase steel in three dimensions utilizing commercial software. The object of the model, multiphase of ferrite and martensite, is known to benefit its fatigue performance by its high toughness yet maintains the high tensile properties due to controlled microstructure. Multiphase steel having a microstructure consisting of polygonal ferrite and martensite has received a great deal of attention due to their useful combination of high strength, high work hardening rate, and ductility. From the fracture mechanics point of view, the key to its fatigue performance is the large plastic zone size in front of the crack. In this research, a sub-modeling technique is used, by using three-dimensional modeling of cube with variation of ferrite fraction as local models. The global model, a compact tension specimen, is treated as a homogeneous material. The results show strong correlation and similarity with that of two-dimensional model. The analysis result shows the variation of the plastic zone sizes as the ferrite fraction varies and saturates at about 60% ferrite fraction.