The Role of Rotations in the Micromechanics of Shape Memory Alloys

Phenomenological theories of martensite establish that because the phase transformations are diffusionless, the foundational framework of continuum mechanics can be used to model their associated deformations. It then follows that these deformations may be decomposed into stretches, rotations, and displacements. For decades the rotations have largely been ignored to simplify micromechanical modeling. However, recent work has shown that while rotations are not critical to some analytic calculations, such as calculating the maximum tensile strain or compression strain that a single crystal may achieve, they are generally essential to correctly predict transformation strains and variant selection using micromechanical models, especially for polycrystals. This work will be presented in examining single and polycrystal superelastic and actuator micromechanics of nickel titanium shape memory alloys.