Numerical modelling of pseudoelastic behaviour of NiTi porous plates

This study presents a computational model for deformation behaviour of near-equiatomic NiTi holey plates using finite element method. Near-equiatomic NiTi alloy deforms via stress-induced A↔M martensitic transformation, which exhibits a typical hystoelastic mechanical behaviour over a stress plateau, known as the pseudoelasticity. In this model, the transformation stress is decomposed into two components: the hyperelastic stress, which describes the main reversible aspect of the deformation process, and the hysteretic stress, which describes the irreversible aspect of the process. It is found that with increasing the level of porosity (area fraction of holes), the apparent elastic modulus before and after the stress plateau decrease, the nominal stresses for the A↔M transformation decrease and the strain increases, and the pseudoelastic stress hysteresis decreases. In particular, the transformation strain increases by about 25% by introducing 32% porosity. Upon loading, the strain in a holey plate made of NiTi is more uniformly distributed than in a steel plate of the same geometry. The majority of steel plate remains in a low strain range, with a small portion highly strained. In NiTi, a large volume fraction of the plate undergoes moderate strains.