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

本研究旨在为形状记忆合金（SMA）低温热源发电系统的组成提供基础数据。在将SMA应用于发电系统的情况下，SMA是在热力-机械循环的条件下与装卸和加热-冷却相结合使用的。在相变温度、变形应力、恢复应力和应变能的影响下，材料的功能和力学性能会发生变化，表现为增大或减小，并出现不可恢复应变和热-机循环双向应变等退化现象。了解SMA的性能变化及其退化特性，对提高SMA在发电系统中的应用寿命具有重要意义。本课题采用不同冷加工值的Ti-Ni-Cu型SMA钢丝试样，利用所建立的热-机械疲劳试验设备进行了热-机械循环试验。实验研究了冷加工对SMA功能和疲劳性能的影响。冷加工是延长疲劳寿命的方法之一，其冷加工比为10 ~ 40%。所得结果总结如下：1。随着冷加工比的增大，变形应力增大，各种转变温度降低，恢复应力随冷加工比的增大而增大。每循环有效应变能随冷加工比的增大而增大。功能降解发生在马氏体相，降解率稳定在高冷加工比。随着冷加工比的增大，热-机循环疲劳的全寿命变短，在整个疲劳寿命中获得的总有效应变能随着冷加工比的增大而减小。热-机械疲劳寿命用分散应变能来评价，分散应变能确定为每循环恢复应变能的减少量。少

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