Nonlinear geometric influence on the mechanical behavior of shape memory alloy helical springs

This paper investigates the nonlinear geometric effect on the mechanical behavior of shape memory alloy (SMA) helical springs. First, the SMA wires are characterized, and then the design and fabrication of SMA helical springs are discussed. Experimental tensile tests are carried out to show the nonlinear geometric influence. Results show a coupling between constitutive and geometric nonlinearities that defines the spring stiffness. Two springs with different geometries are built from SMA wires to define springs with both weak and strong nonlinear geometric influence. Numerical analyses are developed, using the finite element method to confirm the general conclusions shown in our experimental observations. (paper)