Enhancement of Fatigue Properties in Sensor Element by Surface Modification

The fatigue property of TiNi shape memory alloy (SMA) is one of the important issues for its use as a sensor element. In this study, the fatigue life of TiNi SMA was improved by ultrasonic shot peening (USP), which can provide the same or a better effect than general shot peening. The effects of the residual stress, surface roughness, and fatigue crack initiation position on the fatigue life of TiNi SMA wires treated by USP were investigated. The results obtained are summarized as follows. (1) The value of the upper stress plateau under the loading process is increased by USP. The increase in stress is almost proportional to the coverage. (2) In the rotating-bending fatigue test, the fatigue life is improved by USP with coverages of 200, 1000, and 2000%. (3) The higher the coverage, the higher the percentage of fatigue cracks that appear from the specimen surface in USP specimens.