Stress ratio effect on the functional behavior of the pseudoelastic SMA

The effect of stress ratio on the functional properties of a nickel-titanium shape memory alloy was studied. Cylindrical specimens with a diameter of 4 mm were tested under uniaxial tensile cyclic loading in stress-controlled mode. The stress ratios were 0.1 and 0.5, with a frequency of 0.5 Hz in both cases. The experimental results determined the dissipated energy W_dis for both stress ratios 0.1 and 0.5. The dissipated energy increases exponentially up to 7 times with a decrease in the stress ratio under the same load. This result is explained by increased hysteresis loop area at a higher load amplitude. However, the fatigue life of specimens under a stress ratio equal to 0.5 is approximately three times higher than under a stress ratio equal to 0.1 at the same stress range.