MODELING THE TRANSFORMATION STRESS OF CONSTRAINED SHAPE-MEMORY ALLOY SINGLE-CRYSTALS

Shape memory alloys (SMA) are a unique class of engineering materials that can he further exploited with accurate polycrystal constitutive m odels. Previous investigators have modeled stress-induced martensite f ormation in unconstrained single crystals. Understanding stress-induce d martensite formation in constrained single crystals is the next step towards the development of a constitutive model for textured polycrys talline SMA. Such models have been previously developed for imposition of axisymmetric strain on a polycrystal with random crystal orientati on; the present paper expands the constrained single crystal SMA model to encompass arbitrary imposed strains. To evaluate the model, axisym metric tension and compression strains and pure shear strain are impos ed on three SMA: NiTi, Cu-Al-Ni (beta(1)-->gamma(1)) and Ni-Al. Model results are then used to understand the anisotropy and asymmetry of tr ansformation stress in the three SMA considered. Finally, the impact o f the present results on polycrystal behavior is addressed. Copyright (C) 1996 Acta Metallurgica Inc.