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About the choice of a plastic-like model for shape memory alloys

The aim of this paper is to examine the impact of the choice of plasticity theory-inspired model in the prediction of the shape of phase transformation domains. In this field a comparison is made between Huber-Von Mises based model and an another integrating the non-symmetry between tension and compression. The yield surface of phase transformation initiation for an homogeneous body under proportional biaxial loading is discussed. | Vietnam Journal of Mechanics, VAST, Vol. 33, No. 4 (2011), pp. 283 – 291 ABOUT THE CHOICE OF A PLASTIC-LIKE MODEL FOR SHAPE MEMORY ALLOYS C. Lexcellent, R. M. Laydi Département DMA, FEMTO-ST (UMR CNRS 6174) University of Franche-Comté, France Abstract. The aim of this paper is to examine the impact of the choice of plasticity theory-inspired model in the prediction of the shape of phase transformation domains. In this field a comparison is made between Huber-Von Mises based model and an another integrating the non-symmetry between tension and compression. The yield surface of phase transformation initiation for an homogeneous body under proportional biaxial loading is discussed. A transport of these surfaces in the space of the "effective transformation strain of martensite tensor" is given. Key words: Shape memory alloys, phase change, elastic-plastic models, multiaxial behavior. 1. INTRODUCTION The thermomechanical behavior of shape memory alloys SMA can be considered as surprizing towards elasto-plastic classical materials. Two mechanisms can be involved in its loading response i.e. (i) a phase transformation between a mother phase called austenite (generally cubic) and a product phase called martensite (orthorhombic, monoclinic, tetragonal. . . ) (ii) a reorientation process of the martensite platelets. The phase transformation induced by stress action is called "pseudo-elasticity" and the reorientation from self accommodating martensite variants to stress induced ones is said "pseudo-plasticity". Apparently on loading, for instance, the tensile curve σ ↔ ε are the sames than the ones for elastoplastic materials but not the mechanisms involved. The differentiation comes on unloading. For SMA pseudo-elasticity, the behavior is reversible mechanically and irreversible for elasto-plastic (presence of residual plastic strain at stress free state). The comparison on unloading between pseudo-plastic and elasto-plastic material is the presence of caoutchoutic .