Stress induced martensitic transformation kinetics of polycrystalline NiTi shape memory alloy

The variation of semi-empirical volume fraction of martensite as a function of thermodynamic driving force (t.d.f.) is determined based on measurements of pseudo-elastic deformation effects appearing in tubular Ni51at.%-Ti specimens submitted to isothermal biaxial proportional loading. To this end a thermodynamic framework developed by one of the authors (B.R.) was employed. These new experimental results when compared with the predictions of specific formal equations for martensitic phase transformation (p.t.) proposed earlier by B.R., indicate the need for modification of the formula describing the kinetics of reverse p.t. (martensite→austenite) associated with the formation of partial hysteresis in stress-strain co-ordinates. The applied method is new and the results are of importance in macroscopic modelling (determination of appropriate sets of constitutive equations) of the pseudo-elastic behaviour of SMA under complex stress state