Fronts of strain-induced phase transformation and their kinetics

The paper reports on a study of macroscale strain localization in nitinol under tension at room temperature. The specimens were fully austenitic, and therefore, they underwent martensite transition under deformation. It is established that the strain-induced phase transformation occurs through the formation and motion of two strain localization fronts originating at the boundaries of the specimen gage section. The fronts move toward each other with constant velocities and annihilate on meeting. Their velocities are determined by crosshead velocity and stress plateau duration. In this respect, the behavior of the phase transition fronts is completely similar to the kinetics of Luders bands fronts observed in mild steel, but the distinctive feature of this phenomenon is that the level of strain localization at the phase transition front is an order of magnitude smaller than that at the Luders band front.