Effect of loading rate and thermomechanical coupling on fracture of shape memory alloys

Abstract

This work is on the investigation of the effect of loading rate and thermomechan ical coupling on mechanical behavior and fracture of shape memory alloys (SMA). The constitutive model of Zaki and Moumni (ZM) is studied in detail and re-derived. With the changing loading rates, the ZM model does not capture correctly the martensite start stress. Based on experimental works of Tobushi et al., Mutlu and Shaw, a relation is proposed for the martensite start stress, σms to account for a change in loading rate. Some model parameters contain σms as variable, so, they are also proposed to be func tion of local strain rate. For numerical calculations ABAQUS is used and therefore the user subroutine UMAT is rewritten accordingly. Finite element simulations are conducted with modified model parameters using the specimen of Shaw. The stress strain behavior and hysteresis area are compared to the results obtained by using the unchanged ZM model. The fracture specimen, used in Mutlu’s experiments is modeled using original and modified model. Transformation regions, crack mouth opening dis placements (CMOD), temperature fields and stress intensity factors are obtained using original coupled/uncoupled and modified models to investigate effect of loading rate and thermomechanical coupling; the results are compared to experimental ones.