Microstructure and Thermomechanical Behavior of Helical Shape Memory Alloys

Shape memory alloys (SMAs) are known for their exceptionally large energy density and unique thermomechanical behaviors, including the shape memory effect and superelasticity, which can facilitate the invention of novel solid-state actuators and reusable energy absorbers. Helical forms, such as stranded wire rope and tension springs, provide a new opportunity to expand the mechanical design space of available SMA wires to unprecedented large forces and large displacements, respectively, in an economical way. Suitable design and analysis tools, however, do not currently exist. Modeling and simulations of such SMA forms is quite challenging due to the material’s strong thermo-mechanical coupling, nonlinear kinematics, simultaneous deformation modes (extension, bending, and twisting), and the lack of rigorous multi-axial constitutive models for SMAs. To date, experiments on SMAs have at best used surface measurement techniques to interrogate the behavior, but helical SMAs that undergo complex deformations require sub-surface, volumetric strain field and microstructural phase fraction measurements to better validate and inform the development of constitutive models and analysis tools.

We propose to use synchrotron experiments to obtain the texture, strain pole figures, and phase fractions during thermomechanical experiments of SMA cables and tension springs for the first time. If successful, this new volumetric measurement technique should lead to significant advances in the scientific understanding of SMA behavior by clarifying the intrinsic phase transformation kinetics underlying these relatively unexplored forms of SMAs, and it would likely enable the volumetric strain mapping of other more complex and novel SMA devices.

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Project ID: 2022