Abstract
Shape memory alloy (SMA) couplers were prepared from three kinds of Cu-Zn-Al alloy sheets by deep drawing and ironing at 423 K. Its coupling characteristics was tested in the following way. The coupler was expanded at 223 K by inserting a tapered punch and was heated in boiling water to shrink and grasp a bar. It was found that the force required to pull out the bar from the coupler increases with decreaseing Ms temperature. This means that the manufacturing process causes no changes in the initial shape memory properties, such as stress-strain curves of both parent phase and martensitic phase and so on. This test method can detect the characteristics of an SMA coupler. We further obtained the couplers with various thicknesses by a double-sheet-drawing technique using sheets of various hardnesses; the thickness strain of an SMA coupler is controlled through the hardness of its partner material during deep drawing. The test results of the couplers with various thicknesses were contrary to expectation, that is, the pull-out force increases with an increase in the reduction of wall thickness, neverthless the formed couplers all experienced the same shape-memory-heat treatment above the recrystallization temperature. It was found this was caused by the variation in the shape of couplers with the reduction; that is, thick couplers had a bell-bottomed shape because of a lower degree of ironing, and thus thick couplers were subjected to an insufficient expansion ratio.
