A 3D coupled model for SMA composites

In the wide and always expanding world of composite materials, the shape-memory-alloy (SMA) composites are having a more and more relevant role. Incorporating SMA with other structural or functional materials, it is possible to produce "smart materials", able to tune their behavior according with some external stimuli, to exploit the peculiar characteristics of the individual elements to achieve multiple responses and optimal properties. The most common composites are realized introducing SMA wires in a metallic or polymeric matrix. These materials are able to increase the dissipation and resistance capability of the structure as well as to control structure shape changes; hence they are mainly used for displacement, vibration and cracking control. This work studies numerically the mechanical response of a composite in which SMA wires, previously deformed, are embedded in a matrix and are able to recover the original (undeformed) shape through heating (shape memory effect). The thermal increment is obtained imposing a potential difference at the edges of the structure: the electric conduction produces heat through joule effect. The composite 3D model is developed in the frame of the finite element code FEAP by the definition of a user element where the electrical, thermal and mechanical problem are coupled. In particular for the mechanical constitutive law of SMA it has been used the discrete model previously proposed by the authors. Various tests are performed to verify the correctness and the efficiency of the model.