Effect of crimped SMA fiber geometry on recovery stress and pullout resistance

This study investigates the recovery stress and pullout resistance of crimped fiber made by cold drawn shape memory alloy (SMA) wires considering the geometry of the crimped fiber, namely, wave height/depth. Moreover, it assesses how the shape memory effect influences the pullout resistance of the crimped fiber. For this purpose, four types of crimped fibers with different wave heights as well as the as-received fiber without any crimping are prepared with six specimens, and half of them are heated to induce the shape memory effect. The recovery stress is measured with several heating temperatures ranging from 100℃ to 300℃, and the residual stress at room temperature is also measured. When the crimped fibers are heated to induce phase transformation, the ratio of wave height to wire diameter is reduced from 33% to 48%. In this study, two types of crimped fibers with relatively small wave height do not show yielding, while the other two fibers with relatively large wave height show yielding of the fiber. Thus, this study suggests a critical wave depth for yield of the fiber. If the difference between wave height and thickness, namely wave depth, exceeds 0.1 mm, the crimped fibers experiences yield.