PHENOMENOLOGICAL CONSTITUTIVE-EQUATIONS FOR NUMERICAL SIMULATIONS OF SMAS STRUCTURES - EFFECTS OF THERMOMECHANICAL COUPLINGS

Tension-compression tests at different room temperatures and at differ ent strain rates have been performed on Shape Memory Alloys (CuZnAl, N iTi) using a thermomechanical device. The experiments underline the ma in role of the temperature variations induced by the deformation proce ss on the stress-strain curves. These variations are essentially due t o the latent heat of phase change and the analysis of the associated e nergy balances shows that the intrinsic dissipated energy remains very small compared to deformation work or latent heat of phase change. On the basis of these results, a behavioral model is proposed that assum es an intrinsic dissipation identically equal to zero and that conside rs anisothermal deformation processes. This model, written under the f ormalism of Generalized Standard Materials takes into account the ther moelastic couplings and considers two self-accommodating martensite va riants. It is implemented in a finite element code realized to predict the effects of thermomechanical couplings. An implicit integration sc heme is used to derive at each step in time the fields stress, strain, temperature, and volume proportions of phases. At each step and due t o the thermomechanical coupling, we have to solve nonsymmetric linear systems. Numerical simulations are shown first to verify the coherence with the experimental results obtained under uniaxial loading, and se condly to underline the practical interest of such an approach to desi gn SMA's structures.