Two ways for predicting the hysteresis minimisation for shape memory alloys

In a recent communication, James and Zhang proposed four criteria for hysteresis width minimization for alloys exhibiting a first order solid-solid phase transformation. In the present work, four different phase transformations are investigated through four different alloys: cubic -> trigonal R-phase for NiTi, cubic -> monoclinic 14 for Cu-Zn-Al, cubic -> monoclinic I for NiTi and cubic -> tetragonal for Ni-Mn-Ga. The first aim of this paper is to validate the efficiency of these four criteria of reversibility. The second aim of the paper is to show how the crystallographic theory of martensite, built to predict microstructure under stress free state or dead loads, can be used for continuous loadings. Except for Ni-Mn-Ga, the criteria predictions are in good agreement with the experimental observations and with the choice of the Helmholtz free energy function expression. (C) 2007 Elsevier BN. All rights reserved.