Evaluation of Degrading Characteristics of Ti-Ni Shape Memory Alloy under Combined Cyclic Condition of Load, Displacement and Temperature

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The aim of this Study, conducted during two years of 1988 and 1989, is to evaluate the cyclic degrading characteristics of Ni-Ti shape memory alloy under combined cyclic conditions of load, displacement and temperature. In the first year of 1988, an experimental system was developed to investigate the material performance of the Ni-Ti shape memory alloy.And then, by using this testing system, degrading processes in low cycles range were studied precisely on two phases; one was shape memory effect and another was superelasticity. In the second year of 1989, degrading tests in long life range up to 10000 cycles were conducted systematically by adopting resistance-heating procedure, which enable us to conduct thermal cycle tests with period of about 20 sec.Major conclusions obtained through 2 year investigation can be summarized as follows:(1) It was confirmed that the level of performance of the experimental system used in this study to evaluate the.degrading processes of shape memory alloy-was high. (2) Heat-treatment condition to control the shape memory effect predominantly influenced the martensite transformation temperature, and the lower was the heat-treatment temperature the higher was the load level to induce the martensite transformation. (3) Shape memory effect and superelasticity could be kept during long term range when heat-treated at low temperature.