Effect of spherical micro-voids in shape memory alloys subjected to uniaxial loading

Abstract: In this study the effect of micro-voids on the superelastic–plastic behavior of shape memory alloys is investigated. A new constitutive model for porous shape memory alloys, based on the Gurson–Tvergaard–Needleman formulation, is proposed. The model is able to reproduce both forward and reverse stress induced phase transformation, as well as plastic deformation. In addition, the model accounts for the presence of micro-voids and void-growth through a void volume fraction. A one dimensional implementation has been conducted, and results from the new constitutive model is compared with finite element unit-cell analyses. The model does well in reproducing results from unit-cells with void volume fractions . However, some discrepancy is found for void volume fractions that can be attributed to the highly inhomogeneous stress field in the unit-cells which the new model does not account for. The main results show that even for relatively small micro-voids the stress at which transformation and plastic yielding is initiated is lowered. Also, the presence of micro-voids leads to a narrowing of the stress–strain hysteresis which affects the amount of energy dissipated during a superelastic cycle. [Copyright &y& Elsevier]