Effects of Microstructure on the Buckling Fatigue and Functional Degradation Characteristics of the Tape-shaped Cu-Al-Mn Shape Memory Alloy Element

Abstract

Shape memory alloys (SMAs) are functional materials with high shape memory and super elasticity effects that are used in a wide range of fields, including medical and engineering fields. Our research group has focused on the negative stiffness characteristics of plate-shaped SMA during buckling deformation and has attempted to apply them to vibration-isolation devices. The buckling properties of Cu-Al-Mn SMA, which exhibits almost the same super elastic properties as Ti-Ni SMA, were evaluated in comparison with those of Ti-Ni SMA. The results showed that Cu-Al-Mn SMA is more suitable for vibration isolators because of its smaller change in post buckling properties due to temperature change and smaller hysteresis compared with Ti-Ni SMA. In addition, the buckling fatigue and functional degradation properties of Cu-Al-Mn SMA were studied. As a result, it was clarified that fatigue failure is basically caused by the propagation of cracks originating from grain boundaries, and that the increase of these cracks is the cause of the decrease in buckling load. In this study, the buckling fatigue properties of Cu-Al-Mn SMA material in which bainite phase is formed at the grain boundary by changing the heat treatment conditions were investigated, and the effects of the differences in internal microstructures on the buckling fatigue and functional degradation properties of plate-like Cu-Al-Mn SMA with different internal microstructures were compared with those of conventional Cu-Al-Mn material. The effects of different internal microstructures on buckling fatigue and functional degradation properties of plate Cu-Al-Mn SMA with different internal structures were investigated. The results show that the specimens with bainite phase have superior fatigue properties, but in terms of functional degradation properties, they increase the rate of decrease in Pcr and increase the rate of increase in tangential stiffness after buckling.