Abstract:

This paper deals with the effects of the cyclic loading number,the strain amplitude and the loading rate on such mechanical behaviors of shape memory alloy wires as the phase transformation stress,the energy consumption per cycle,the deformation modulus,the equivalent damping ratio and the residual strain.Experimental results show that（1） at a certain loading rate,both the forward and the inverse transformation stresses decrease with the increase of the cyclic loading number,especially the former;（2） the forward transformation stresses tend to be stable after 20 cycles,while the inverse ones be stable after only 5 cycles;（3） with the increase of the cyclic loading number,the energy consumption per loading cycle decreases and the amplitude is up to 33% when the cyclic number increases from 1 to 30;（4） the residual strain increases with the increase in the cyclic loading number till to the saturation value of 0.4% after 30 cycles;（5） the equivalent damping ratio increases with the strain amplitude till to the maximum at a strain amplitude of 7%,then it slightly decreases,while the unloading modulus decreases with the increase in the strain amplitude;and（6） the loading rate affects not only the transformation stress but also the energy consumption-specifically,with the increase in loading rate,the transformation stress increases,while the energy consumption slightly decreases.

Key words: shape memory alloy, NiTi wire, superelasticity, mechanical behavior, stress-strain