Shape Memory Alloys (SMA) belong to a special group of metallic materials, which are capable of returning to a pre-determined shape or size when submitted to an appropriate thermal cycle. Generally, these alloys can be easily deformed at a relatively low temperature and, when exposed to a higher temperature, can return to their original shape, that is, to the shape they had before the mechanical deformation was imposed. Although there are a vast variety of materials that can achieve the Shape Memory Alloy effect, only those in which it is possible to have a significant recovery of the deformation – or in which it is possible to generate an important force during the shape's change – can be functionally and commercially interesting. The Ni-Ti alloys, which are one type of SMA, were numerically modelled through Ansys software and these studies are presented in this paper. These special alloys, among many others applications, could be used, for instance, in the form of wires (fibres), in smart composites, as actuators to recover partially the structural integrity of a matrix with cracks. Some 2D and 3D cracked plates were modelled through finite elements and the Stress Intensity Factor, in Mode I, KI, at each crack tip, was determined and compared with the result obtained through the analytical solution. Wires of Ni-Ti, with very small diameters and with different length/diameter ratios, were modelled and mechanical load cycles, at different temperatures, were applied and the material’s behaviour/response was obtained. The thermo-mechanical behaviour of the material was defined based on results published by other authors. Also, a composite material with Ni-Ti fibres embedded was modelled and a mechanical load was applied to it.