A Discussion on the Mechanical Properties of Shape Memory Alloys Based on a Polycrystal Model

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Abstract
The scheme previously proposed by the authors on the basis of the Taylor model to deal with the deformation of polycrystals caused by the stress induced martensitic transformation (SIM) has been futher extended to describe the recovery stress associated with the reverse transformation upon unloading. According to this scheme, the “modified” Taylor factor M′ has been calculated as a function of grain orientation for the cases of tensile and compressive deformation in shape memory alloys such as CuZnAl, CuAlNi and TiNi. The results demonstrated the difference in the plastic anisotropy for SIM of grains under the polycrystalline constraint from that of isolated crystallites. The strain hardening due to the internal stresses caused by the grain orientation dependence of volume change has been shown to be insignificant in these alloys. General discussion has been given to the yield stress, recovery stress, pseudoelastic hysteresis, recovery strain, ductility, and strain hardening of the shape memory alloys, in relation to the magnitude and orientation dependence of M′.