Exploration of static equilibrium in elastically biased shape memory alloy components

In the past, several studies have explored the fundamentals and applications of deforming an elastic component using a shape memory alloy (SMA) component. Previous explorations have been primarily motivated by the capability of SMA actuation against a spring biasing load and dynamic response where energy dissipation upon perturbation or thermal tunability is desired. This current work instead explores elastically biased SMA components in the context of a static system, where both stress-induced and thermally-induced phase transformations are employed to reproduce and improve upon the advantages of the shape memory effect (SME). While deformation of an SMA component utilizing stress-free SME can only be mechanically generated and thermally recovered, a system composed of an elastically biased SMA component can generate and recover deformation both mechanically and thermally. Additionally, the applied stress necessary to induce deformation is thermally tunable in both systems, but the non-zero stress state of the elastically biased SMA component enables operation at higher temperatures. This study also introduces employing the same antagonistic concept as a low power intensive two-way actuating system that utilizes “impulsive” heating and cooling to generate and recover deformation, while the balance of internal reaction forces enables deformation to be maintained. In this work, experimental and finite element analysis (FEA) results will demonstrate the capabilities of an SMA component biased against a cantilevered beam composed of elastic material. The results from this investigation will also introduce an abstraction termed the equilibrium domain, which represents the range of equilibrium points in stress-strain-temperature space.