Two parameter characterization of edge cracked NiTi shape memory alloy under plane strain conditions

Shape memory alloys (SMAs) are metallic systems that exhibit reversible,diffusionless,martensitic phase transformation. Employing finite element analyses, the stress fields and crack tip constraints generated are examined for a NiTi SMA which exhibits superelastic behavior. For this purpose, a single edge cracked configuration satisfying plane strain conditions is subjected to uniform loading. Both pure Mode I and mixed mode (Mode I + Mode II) configurations are elaborated by changing the crack inclination angle. As a novel step, a multi-parameter fracture mechanics approach is adapted to characterize the dependence of stress field components on both asymptotic r^(-1/2) and radial r^0 terms around the crack tip. This task is accomplished by generating closed-form fitting expressions for stress components via nonlinear least-square regression of the full field data from finite element analyses. It has been shown that r^0 term plays a significant role on the stress field around the crack tip in NiTi SMAs.