: Shape memory alloys (SMAs) are a class of smart materials with the intrinsic properties of shape memory effect (SME) and pseudoelasticity (PE) due to their solid-solid martensitic phase transformations under various thermomechanical loadings. The pure torsional low cycle fatigue of pseudoelastic shape memory bars in different rotational speeds (i.e. frequency) is studied in this thesis. Indeed, the research domain is confined to pure torsion, low cycle fatigue and pseudoelasticity. Other subjects such as uniaxial or high cycle fatigue and SME either are studied adequately or require no particular investigations. One of the drawbacks in studying cyclic behavior of these alloys is the absence of a capable constitutive model to predict their behavior; thus, most of the available results have been experimentally achieved. In this regard, the only existent and used constitutive model is formed on the base of experimental observations and not in a continuum framework. This model has predicted fatigue life with the use of a parameter called stabilized dissipated energy. On the other hand, there is a lack of constitutive relation to correlate stress and strain in different loading conditions, for instance torsion, bending or 3-D loadings in general since most of the models are developed for uniaxial tensile loadings. In the present work, an enhanced extended one-dimensional constitutive model is assumed to describe the shear stress-strain response by means of von-Mises yield criterion. In other words, the concepts of effective stress and strain are properly employed to derive shear stress-strain relation based on a 1-D model for axial loadings. Moreover, a fully-coupled thermomechanical model which is presented in a continuum framework is employed to predict the sample behavior, and results of this model are compared with experimental findings to verify the model. As a result, a relation for fatigue life of the studied SMA is generated with the stabilized dissipated energy’s formula, and the numerical results are shown to be in a good agreement with experimental data indicating validity of the proposed approach. Finally, the influence of the test parameters such as angle of rotation, temperature, specimen geometry and loading frequency on the fatigue life are investigated Keywords: Shape memory alloys, Fatigue life, Low cycle fatigue, Stabilized dissipated energy, Loading frequency, Torsional loading, Pseudoelasticity.
