Study of the shape memory effect in lamellar helical springs made from Cu–Zn–Al shape memory alloy

The behavior of helical springs made from lamellar specimens of Cu–Zn–Al shape memory alloy, which were martensitic at room temperature, was analyzed in force–elongation–temperature space. The study revealed the dependence of two forms of shape memory effect (SME): (i) work-generating SME and (ii) constrained-recovery SME, upon applied load and elongation, respectively. The tensile behavior of the springs, on loading between the austenite-start and the austenite-finish temperatures showed a stiffening tendency with increasing both elongation and temperature. The lamellar helical springs were able: (i) to lift 3 N loads over 0.235 m with a rate of 7 × 10−3 m/K; (ii) to develop with a maximum rate of 0.6 N/m a recovery force as high as 24 N while being elongated by 0.232 m; (iii) to elongate by 7 × 10−2 m under the effect of a 20 N force applied at 328 K, with an average rate of 342 N/m.