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-st rain-temperature specially developed apparatus. The evolution of the s tress-strain curves with time was followed in partially transformed sp ecimens, having several martensite plates, all of the same variant. Ex ponential type behaviour was observed, and four different time constan ts were obtained from experiments performed under particular condition s. A physical interpretation could be suggested for all of these param eters. They are related to the evolution of the Ms with the time elaps ed from the thermal treatment, the martensite stabilization and the be ta-recovery. Some of these time constants were found to be dependent o n the presence and movement of the beta-martensite interfaces. A model based on the experimentally determined parameters was developed, whic h allows to simulate the observed time-dependent behaviour.