Effects of Pre-Damage on HCF Behaviors of Ti-6Al-4V Alloy

Abstract

The effects of pre-damage on the fatigue strength of Ti-6Al-4V were investigated by applying the low cycle fatigue(LCF) as a pre-damage prior to high cycle fatigue(HCF) test. The fatigue strengths were obtained by means of step-loading method. The pre-damage condition was decided as 900MPa, 0.5R, 50,000 cycles through LCF test, and was introduced before step-loading test. The fatigue strength of Ti-6Al-4V alloy derived from step-loading test without pre-damage was about 639MPa. The introduction of pre-damage deteriorates the fatigue strength about 6%. Progressive change in elongation with increasing cycles was observed. The strain accumulated by pre-damage varies the displacement in the next loading step, but afterward this doesn't change the displacement any more. The strain formed by pre-damage is thought to result in earlier failure and lower fatigue strength.