Multiaxial Shape Memory Effect and Superelasticity

Abstract: The specific behaviour of shape memory alloys (SMA) is due to a martensitic transformation [Shape Memory Materials. Cambridge University press, Cambridge]. This transformation consists mainly in a shear without volume change and is activated either by stress or temperature. The superelastic behaviour and the one‐way shape memory effect are both due to the partition between austenite and martensite. The superelastic effect is obtained for fully austenitic SMA: loaded up to 5% strain, a sample recovers its initial shape after unloading with a hysteretic loop. The one‐way shape memory effect is obtained when a martensitic SMA, plastically deformed, recovers its initial shape by simple heating. Superelasticity and one‐way shape memory effect are useful for several three‐dimensional applications. Despite all these phenomena are well known and modelled in 1D, the 3D behaviour, and especially the one‐way shape memory effect, remains quite unexplored [Mater. Sci. Res. Int., 1 (1995) 260]. Actually, the development of complex 3D applications requires time‐consuming iterations and expensive prototypes. Predictive phenomenological models are consequently crucial objectives for the design and dimensioning of SMA structures. Therefore, a series of 2D proportional and non‐proportional, isothermal and non‐isothermal tests have been performed. This database will be used to build a phenomenological model within the framework of irreversible processes.