Shape memory alloys (SMAs) are widely used in various areas such as aerospace, medicine and robotics. These applications are indebted to their two significant characteristics of shape memory effect (SME) and pseudoelasticity (PE). Shape memory effect is said to the reversible permanent strain by heating, and pseudoelasticity is the full recovery of strain during loading and unloading at high temperatures. These unusual characteristics are due to change in the crystal structure of material during transformation between the high-temperature phase, austenite, and the low-temperature phase, martensite. Since these alloys are mostly used in the form of wire, it is necessary to study their behavior in this case as well. In this thesis, the behavior of an SMA wire in simple tension test is simulated by a 3-D model with the presence of grippers. Since preparing shape memory alloys with the usual standard geometry in tension test is not possible, it is important to model these alloys in the form of wire. Moreover, due to the dependence of the material behavior on stress, considering the grippers and their stress concentration are notable in tension test of shape memory alloys. In this study, in order to achieve a reliable model, the initial models run and the results are compared with the existing results. Then, the three-dimensional UMAT of SMAs, that has been previously developed based on the Brinson model, is studied with the simple models. The finalized model is developed based on Kamrani's experiments and model, and the elastic and elasto-plastic material behaviors are first investigated. Then, the shape memory alloy model is simulated by using the UMAT, and the results are compared with the Kamrani's findings. At last, to improve the results, a new UMAT is developed similar to the elasto-plastic behavior by considering the effect of material softening during the transformation. Additionally, the new UMAT is employed in the model, and the results are compared with those reported by previous investigators Keywords: Shape memory alloys, Tension test, Simulation, Gripper
