HYSTERESIS IN CU-ZN-AL SMA - FROM HIGH-RESOLUTION STUDIES TO THE TIME-DEPENDENT MODELING AND SIMULATION

The role of diffusional processes, time and temperature dependent, on the hysteretic behaviour was studied using a high resolution stress-strain-temperature specially developed apparatus. The evolution of the stress-strain curves with time was followed in partially transformed specimens, having several martensite plates, all of the same variant. Exponential type behaviour was observed, and four different time constants were obtained from experiments performed under particular conditions. A physical interpretation could be suggested for all of these parameters. They are related to the evolution of the Ms with the time elapsed from the thermal treatment, the martensite stabilization and the beta-recovery. Some of these time constants were found to be dependent on the presence and movement of the beta-martensite interfaces. A model based on the experimentally determined parameters was developed, which allows to simulate the observed time-dependent behaviour.