Basic Study of Electric Generation with Low Temperature Heat Source by Shape Memory Alloy(Thrmo-Mechanical Cyclic Properties and Lengthening of Fatigue Life)

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This research is aming to obtain the basic data for composition of the electric generation system with low temperature heat source by shape memory alloys (SMA). In the case of applying the SMA to the electric generation system, the SMA are used under the conditions of thermo - mechnaical cycling in combining with loading-unloading and heating - cooling. And, the functional and the mechanical properties change such as increase or decrease in the transformation temperature, the derfomation stress, the recovery stress and the strain energy and also, the degradations arise such as appearance of the irrecoverable strain and the two-way strain with thermo-mechanical cycling. It is very ipmortant to know the properties changes and the degradation chnaracteristics, and to make the lengthening of fatigue life of the SMA for appling the SMA to the electric generation system.In this research project, Ti-Ni-Cu type SMA wire specimens with several values of cold-working were used for the thermo-mec … More hanical cyclic tests by using the established thermo-mechnaical fatigue testing equipment.. And the effects of the cold-working on the functional and the fatigue properties of the SMA were investigated experimentally. The cold-working was one of the methods of lengthening of fatigue life, and the conditions of the cold-working ratio were 10〜40%. The results obtained were summarized as the followings.1. The deformation stress increased and the all kinds of transformation temperature decreased with increase in the cold-working ratio, and then, the recovery stress increased with the cold-waoking ratio.2. The available strain energy per cycle increased with increase in the cold-working ratio.3. The functional degradation arised in the martensitic phase, and the the degradated ratio was stabilized in the high cold-working ratio.4. As whole life of the thermo-mechanical cyclic fatigue became shorter with increase in the cold-working ratio, the total available strain energy obtained in the whole fatigue life decreased with increase in the cold-working ratio.5. The themo-mechanical fatigue life was evaluated by the disperted strain enrgy which was determined as the decrease in recovery strain energy per cycle. Less