HYSTERESIS BEHAVIOR OF THERMOELASTIC ALLOYS - SOME SHAPE-MEMORY ALLOYS MODELS

The hysteretic behaviour of shape memory alloys (SMA) needs a more and more thin analysis because of its importance for technological applic ations. The comparison between different approaches allows to explicit e the specifity of every model (macroscopic approach, micro-macro leve l, local description, phenomenological approach) and their points of c onvergence. On one hand, a thermodynamic treatment with a free energy expression as a mixing rule of each phase (parent or austenite phase a nd martensite) by adding a coupling term : the configurational energy, allowes modelling of material hysteresis loops. On the other hand, a phenomenological treatment based on a local investigation of two singl e crystals with a visualisation of microscopic parameters allows to pe rceive the phase transition mechanisms (nucleation, growth). All the o btained results show the importance of entropy production (or of the d efinition of the configurational energy term) for the correct descript ion of hysteresis loops (subloops or external).