Shape memory alloy strands as cross-ties: Fatigue behavior and model-cable net tests

Abstract

NiTi Shape Memory Alloy (SMA) has the potential for use as cross-ties to mitigate cable vibration due to its superelasticity and high damping capacity. However, recent studies revealed that the fatigue problem of the NiTi SMA should be addressed. This paper investigates the fatigue characteristic of SMA strands. The superelastic and structural fatigue characteristics of SMA strands were tested under uniaxial cyclic tensile loading at different strain amplitudes. The maximum stress, residual strain, and dissipated energy were derived from a superplastic fatigue test with 2000 cycles. The test results showed that the parameter values related to the superelastic behavior of the SMA strand decreased in the early stage and then stabilized. A structural fatigue test conducted at strain amplitudes of 0.3% to 2.5% indicated that the structural fatigue life of the SMA strand decreased with increasing strain amplitude; the fatigue life reached two million cycles at the strain amplitude of 0.3%. The free vibration test result indicated that the SMA cross-tie significantly increased the frequency and moderately increased the damping ratio of the cable net. An optimal cross-tie location existed in each vibration mode with the maximum damping ratio.