Modelling of materials with shape memory effect with using finite element method

Materials with shape memory effect exceed conventional materials especially in high reversible deformations (pseudoelasticity) and a possibility of permanent deformation disappearance after applying a heat on them (shape memory effect). The purpose of this article is to define a procedure to acquire characteristic mechanical constants of these materials in order to use Auricchio's material model in FEM software MSC.Marc. A sample in the form of a wire made of the binary NiTi alloy was subjected to tensile test. From the gained stress-strain function the needed values were evaluated. Because of the mechanical properties are strongly temperature-dependent, the tensile tests were performed under various temperatures: 19 degrees C, 37 degrees C, 60 degrees C and 80 degrees C. Dislocation of a hyperelastic plateau up to higher stresses with increasing temperature is clearly visible. Variation of Young's modulus of both phases (austenite, martensite) which the material is passing through during loading and unloading of the sample is also obvious. The conditions of tensile test were simulated in MSC.Marc and gained graph was compared with experimental data. These results will be used for creating a finite element model of endovascular stent. Another advantage of NiTiNOL is, among the other ones, its excellent biocompatibily.