Cyclic stress-strain response of superelastic Cu-Al-Mn alloy single crystals

Stress-strain response of cyclic superelastic deformation was examined in Cu-20at.%Al-10at.%Mn shape memory alloy single crystals. As the superelastic deformation was repeated, the critical stress for the onset of stress-induced transformation decreased at an almost constant rate to zero by a finite number of cycles N-c. By further cycles residual martensite was accumulated until all the stress-induced martensite was left after unloading. The decrease of the stress per cycle and the number N-c depended on the direction of applied stress, i.e. tension, compression and tension-compression, and also the crystal orientation. These N-c's can be related by a linear S-N curve; log N-c decreased linearly with increasing log Delta sigma, where Delta sigma is the hysteresis-width in superelastic stress-strain curve. The observed fatigue behaviour can be understood in terms of internal stress of dislocation substructure formed during the cycles. (C) 1999 Elsevier Science S.A. All rights reserved.