DEFORMATION OF A SHAPE MEMORY ALLOY HELICAL SPRING - (ANALYSIS BASED ON STRESS-STRAIN-TEMPERATURE RELATION)

In the design of a shape memory alloy helical spring, a basic method of designing the spring based on the stress-strain-temperature relation of the material is an important problem to be solved. In the current study, the deformation behavior of the shape memory alloy helical spring was analyzed based on stress-strain-temperature relation of the material. The relationship between load and deflection of the spring as well as the behavior of transformed region is discussed. The main results are summarized as follows. (1) The relation between the load and deflection of the spring is represented by using a simple model of the stress-strain-temperature relation. (2) For a certain maximum deflection, recoverable force and recoverable strain energy increase with temperature. Dissipated strain energy takes a maximum value at a certain temperature. (3) The transformed region in the cross section of the wire expands into the center from the surface under the loading process, but contracts toward the surface under the unloading process. For a certain maximum deflection, the transformed region is small but the load increases as the temperature increases.