Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State

Abstract

Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs) subjected to mode-I, isothermal loading is studied using finite element analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite element suite and crack growth under displacement boundary condition is investigated for plane strain and plane stress conditions. Parameters for the SMA material constitutive law implemented in the finite element setup are acquired from characterization tests conducted on near-equiatomic NiTi SMA. Virtual crack closure technique (VCCT) is implemented where crack is assumed to extend when the energy release rate at the crack-tip becomes equal to the experimentally obtained material-specific critical value. Loaddisplacement curves and mechanical fields near the crack-tip in plane strain and plane stress cases are examined. Moreover, a discussion with respect to the crack resistance R-curves calculated using the load-displacement response for plane strain and plane stress conditions is presented.

Stable crack growth in NiTi shape memory alloys: 3D finite element modeling and experimental validation

“…Moving towards the middle, the stress state tends to plane strain and σ zz has its maximum value at the middle. In this case, the maximum shear stress occurs in planes normal to the plane of specimen and making 45°with the crack plane [44]. Although the variation of G I through the thickness may imply that the crack grows faster in the middle, crack front is found to remain straight during crack growth simulations which agrees with the post mortem examination of the fracture surfaces [23,25].…”