The Effects of Geometric Parameters Under Small and Large Deformations on Dissipative Performance of Shape Memory Alloy Helical Springs

This paper presents an investigation into shape memory alloy (SMA) springs considering the effects of geometry changes under small as well as large deformations. Helical springs were fabricated by shape setting of NiTi wires through heat treatment. The products exhibited pseudoelasticity at the ambient temperature, and their force-displacement responses were examined by performing simple tension tests. A model was further proposed to study tension and compression of SMA springs, and it was shown that the consequences of geometrical changes in tension and compression of springs are different. The numerical results of large and small deformation models were verified by experimental tensile results. In order to design a spring with maximum dissipative performance, a designer has three geometric parameters to set: wire diameter, spring diameter, and the number of active coils. The influences of these parameters on dissipated energy were studied in both displacement- and force-control loadings, and a framework for designing SMA springs with the purpose of achieving maximum applicable dissipation was at last developed.