Fatigue thresholds of Ni-Ti alloy near the shape memory transition temperature

✍ Scribed by R.L. Holtz; K. Sadananda; M.A. Imam

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 741 KB
• Volume: 21
• Category: Article
• ISSN: 0142-1123
• DOI: 10.1016/s0142-1123(99)00065-1

✦ Synopsis

The fatigue thresholds of nickel-titanium alloy with martensite start temperature of 80°C were measured in air from room temperature to 150°C and load ratios of 0.1 to 0.9. The ⌬K versus K max fundamental threshold curves are characteristic of ductile metals at all temperatures tested and are consistent with the existence of two threshold parameters, ⌬K th * and K max,th *, for cyclic and maximum stress intensity, respectively. ⌬K th * increases linearly with temperature, while K max,th *, exhibits a transition between 80 and 100°C, decreasing by half as a function of temperature. Compliance curves suggest the existence of crack closure in the stable martensite regime below 100°C, but little or no crack closure in the stress-induced martensite regime above 100°C up to 150°C. The results suggest that both crack closure and the existence of an intrinsic fundamental threshold curve with both ⌬K and K max thresholds as a function of load ratio are necessary to fully account for R dependence of ⌬K th .