Constitutive model for superelastic shape memory alloys considering strength and stiffness degradation and residual strain: An empirical approach for engineering applications

Abstract

In this work, a novel uniaxial multilinear model for superelastic shape memory alloys that considers stiffness and strength degradation, and residual strain is proposed. To develop it, the results of several tensile cyclic tests at both constant and incremental strain amplitudes on 1.4 mm-diameter CuAlBe wires were used. Thus, degradation models were constructed from statistical correlation between the cycle maximum strain and the deterioration of the mechanical properties: strength, stiffness, and residual strain. Results show that the properties degrade exponentially as the cycle maximum strain increases. The model is validated with experimental data from the literature, showing high accuracy in predicting the evolution of residual strain, modulus of elasticity, transformation stresses, dissipated energy, and damping ratio. Furthermore, the proposed methodology shows a good fit when applied to experimental tests with NiTi bars performed by other authors, demonstrating that it can be extended to other alloys with flag-shaped hysteresis. The engineering-oriented model presented, stands out for its simplicity and accuracy in estimating the complex phenomena associated to superelasticity in SMA, even if random loading paths are imposed.