Modeling the cyclic shape memory and superelasticity of selective laser melting fabricated NiTi

Shape memory alloys (SMAs) have found several industrial and biomedical applications due to their superior mechanical and biological properties. Since SMA devices may experience several cyclic loadings during their function, assessment of their cyclic response is of vital importance. In this paper, an existing constitutive model based on small strains is generalized to investigate cyclic response in superelastic and shape memory regimes of additively manufactured NiTi. To do so, Microplane theory is utilized to calculate the elastic and transformation strain tensors while the associated flow rule is used in combination with linear isotropic hardening for plastic strain tensor. In this model, all the material parameters can be obtained using DSC, the stress-strain response in the first loading-unloading cycle, and the accumulated stress-strain curve. To validate the model, superelastic and shape memory NiTi compression samples are fabricated using selective laser melting. All the specimens are tested in stress-controlled cyclic tests at a constant temperature. The obtained cyclic stress-strain response is compared with the numerical results. The model predicts and the experimental results verify that the residual strain, peak strain, and dissipation energy converge to specific values.