Effect of deformation rate on the axial joint strength made of Fe-SMA

Abstract

Iron-based shape memory alloys (Fe-SMA) have been applied to structural members, such as pipelines and curved pipes, for underground structures due to their excellent properties. However, in the case of an earthquake or high winds, the resulting impact force causes a bending and twisting behavior in joints of the pipe. For this reason, a clear understanding of the relation between the deformation rate and joint strength is strongly needed. In this work, the specimen of a joint which a round bar made of SUS304 is tightened by a hollow cylinder made of Fe-SMA was prepared by first expanding the cylinder at a constant quasi-static rate and heating it up to the austenitization temperature. Then, a push-out test, which a compressive-shear combined force acts, was conducted at various deformation rate including the impact level to evaluate the axial joint strength. The results scientifically demonstrate that the axial strength would show the negative sensitivity with respect to deformation rate. However, when the deformation rate exceeds 8.3 mm/s, positive rate sensitivity can be found. This work may provide us with a systematic understanding of the deformation behavior of joints made of Fe-SMA and the safety design of the product.