Size and Surface Effects in Shape Memory Alloys

I am a PhD student at Northwestern University, working with Prof. Cate Brinson, Prof. David Dunand and Prof. Aaron Stebner. I am looking to graduate in 2017 and primarily looking for R&D based industry positions. I work primarily on polycrystalline NiTi based SMAs, from the macroscale to sub-grain scale, using empirical and modeling techniques. My two major projects have involved studying granular constraints in SMAs in terms of

i. Size Effects ii. Surface Effects.

Size effects are studied as a competition between structural (holes) and microstructural (grain morphology) features during superelastic tensile loading. The key findings show a strong influence of structural features when they are significantly larger than the grain size and a complete dominance of microstructural features when they are of comparable size. On the modeling front, a phenomenological macro-scale model is used to capture the structural effects and compared to strain fields obtained from DIC, while a micromechanical model is used to study granular constraints in neighborhoods close to the structural features, using crystallographic inputs obtained from EBSD.

The surface effect study is towards quantifying a difference in behavior of similar grains on the surface versus in the interior of the sample. High energy x-ray diffraction microscopy and EBSD are used to study the grain and sub-grain level behavior of the material and complimented by crystal plasticity based modeling, to study the effect of different granular constraints on the surface and interior in terms of availability of martensite variants and slip systems for similarly oriented grains.