The role of fatigue variability in life prediction of an α plus β titanium alloy

The fatigue life variability of the alpha+beta titanium alloy, Ti-6Al-2Sn-4Zr-6Mo increased with decreasing stress level. The variability in life was found to be due to segregation of lives due to two failure mechanisms. A bimodal cumulative distribution model was shown to accurately describe the combined failure modes. The nominal failure processes for the two regimes were similar, with crack nucleation occurring in equiaxed alpha(p) particles, irrespective of life or stress level. However the variability in life was not controlled by the size of the crack-nucleating alpha(p), but rather by the ability of the material to distribute deformation and avoid early crack nucleation.