Cyclic Tests in Pushing and Pulling Actions of SMA Rings in Superelastic or Martensitic States

Abstract

Applications of shape memory alloys (SMAs) in engineering generally use bars or wires. However, they should be used only in tension since bars possess risk of buckling and wires do not have any resistance to compression. Thus, they cannot be used in pushing as well as in pulling actions. To overcome this problem, SMA rings are becoming more popular as an alternative element in pushing and pulling actions for smart devices. This study prepared SMA rings in superelastic or martensitic states and conducted cyclic tests in pushing and pulling directions. The outside diameter of rings and thickness were 70 mm and 4 mm, respectively. A special device was designed for the tests and solid bars and plates were used to provide gripping. The SMA rings in the pulling action were loaded by combing bending and tension while they were used together for bending and compression with a pushing action. The SMA rings showed different behaviors in pushing and pulling actions. This difference in behavior may have been caused by the secondary moment due to the P-delta effect. As expected, the superelastic SMA rings showed good self-centering capacity, and the martensitic SMA rings showed a large area of stress-strain hysteresis. Thus, the superelastic SMA ring could be used for self-centering devices, and the martensitic SMA ring can be used for energy dissipation devices.