Modelling of magneto-mechanical behaviour of Ni-Mn-Ga single crytals

Reviews on the various models to describe the quasi-static magnetic-field-induced strains available in the literature are summarised. Two constitutive models, namely the Three-Segment model and Single Segment Model, are formulated aimed at predicting the quasi-static cyclic magnetic-field-induced strain under zero and non-zero stress bias. These two models provide reasonable correlation with experiments available in the literature. Some of the advantages of these two models are that they are in constitutive format, with low-order terms (second order) and hence are readily usable in the modelling of magneto-mechanical coupling effects such as in Finite Element formulations. The parameters of these two models are derived from the magnetisation and mechanical stress-strain behaviour of the material, and hence are readily obtainable from simple magnetisation and mechanical stress-strain tests. The magnetic-field-induced strain is then transformed into different orientations in three-dimensional space using strain tensors, based on certain assumptions, in order to apprehend the theoretical possibilities of magnetic-field-induced strain combinations in this material. It was shown that by varying the orientation of the twin-boundaries of the material, vast combinations of axial and shear magnetic-field-induced strains can be realised. The potential applications of this material are thus broadened dramatically. (c) 2004 Elsevier B.V. All rights reserved.