Pulsating stress controlled low cycle fatigue behavior of Ti-6A1-4V Alloy

Pulsating low cycle fatigue tests of Ti-6Al-4 V alloy which is thought to be a candidate of structural material at cryogenic temperature have been conducted in a stress controlled condition at 77 K and room temperature. Attention was paid to the S-N relation using normalized maximam stress and changes in cumulative plastic strain and plastic strain range during fatigue. The normalized maximum stress was found to be a key parameter by which the difference of test condition, such as temperature, or the deviation of material property can be evaluated in the same S-N relation. The fracture type of this alloy was found to be divided into quasi-static fracture and fatigue fracture respectivily depending on the magnitude of applied load. This was verified by fracture surface observations. It was found that the resistance to failure in the criteria of both stress and strain at 77 K is higher than that at room temperature.