SUMMARY

Shape memory alloys (SMAs) are studied in a variety of length scales ranging from macroscale to nanoscale. In macroscale, a phenomenological constitutive framework is adopted and developed by adding the effect of phase transformation latent heat. Analytical closed-form solutions are obtained for modeling the coupled thermo-mechanical behavior of various large polycrystalline SMA devices subjected to different loadings, including uniaxial loads, torsion, and bending. Using an infrared thermovision camera, various experiments are performed on some SMA devices and the temperature changes are measured during the phase transformation for validating the theoretical results. In order to study some important properties of polycrystalline SMAs that the macroscopic phenomenological frameworks cannot capture, including the texture and intergranular effects in polycrystalline SMAs, a micromechanical framework with a realistic modeling of the grains based on Voronoi tessellations is used. Some experiments on the bending of NiTi micropillars are designed for validating the theoretical results in this section. For studying some aspects of the thermomechanical properties of SMAs that cannot be studied neither by the phenomenological constitutive models nor by the micromechanical models, molecular dynamics and molecular statics simulations are used in nanoscale. Results of this section will be connected to the micro- and macro scale studies by studying the modeled responses at the atomistic level with the assumed response in larger scales.