Two-dimensional modeling to compute plastic zone in front of compact tension sample of a multiphase material

Abstract

More and more components subjected to dynamic high stress loading are heat treated to get multiphase microstructure as their final products, instead of conventional tempered martensite. It is gaining popularity due its manufacturing benefits, including the elimination of the tempering process, and its better fatigue performance. Multiphase of ferrite and martensite benefits its fatigue performance by its high toughness yet maintains the high tensile properties due to controlled microstructure. The plastic zone size in front of the crack is the key to fatigue performance. In this research, a multiphase (polygonal ferrite and martensite) microstructure was developed. Manipulation method to use commercial software to calculate the plastic zone size in front of a crack is presented. Two-dimensional modeling of squares having variation of ferrite fraction was used as local models. The shape of the ferrites was derived from actual microstructure of multiphase material. These local models were put in front of the CT specimen in a global model. The analysis result shows the variation of the plastic zone sizes as the ferrite fraction varies and saturates at about 65% ferrite fraction.