On the Micro-deformation Mechanism of Shape Memory Alloy under Complex Thermo-mechanical Loading Conditions and its Applications

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Summary of Research Results : The present industrial/engineering application of shape memory alloy has been rather limited to the uniaxial deformation, e.g., the simple linear actuating movement using the simple elongation-contraction. On the other hand, the shape memory alloy can be expected to deform in more complex and elegant way, judging from the fundamental deformation mechanism of shape memory alloy. That is, the fundamental deformation mechanism of shape memory alloy is the martensite phase transformation (and its reverse phase transformation). This phase transformation is controlled by 7 independent- parameters, that is, the temperature and the stress tensor whose number of independent components is 6. The aim of this research work is to investigate fundamentally and systematically the role of 7 parameters and to develop the industrial applications of shape memory alloy, for examples, the three-dimensional actuator, complex device, intelligent material systems using these actuators and devices. In this research work, the various kind of combined loads of axial force and torque were applied to the thin-walled tubular specimen of Cu-based shape memory alloy and the corresponding deformation performances were observed. Moreover, the new microscopic observation system was constructed, and the behavior of martensite variant under complex loading conditions was observed. In these fundamental experimental investigations, numerous important data were collected, which are very important for the analysis of the relationship among the nucleation, growth and disappearance of martensite variant in the crystal grain under the complex loading conditions.