A defect-based critical plane method for multiaxial high cycle fatigue life prediction in L-PBF Ti-6Al-4V alloy

A multiaxial high cycle fatigue (HCF) life prediction method is proposed for the laser powder bed fusion (L-PBF) Ti-6Al-4V alloy by integrating the defect-based critical plane method with the Theory of Critical Distances (TCD). The typical defect size inducing fatigue failure is determined by extreme value statistics. The critical plane damage parameters based on the dominant failure modes are selected for accurate life prediction. For materials exhibiting tensile-dominated failure, the critical plane is defined as the maximum opening stress plane, and the Smith-Watson-Topper (SWT) parameter modified by the effective crack driving force is combined with the TCD to predict life. For materials exhibiting shear-dominated failure, the critical plane is defined as the maximum shear stress plane, and the Fatemi-Socie (FS) parameter modified by the effective crack driving force is coupled with the TCD to predict life. The proposed method is validated using fatigue test data of L-PBF Ti-6Al-4V alloys subjected to diverse post-processing treatments. The results demonstrate that 92% of the predicted life points fall within ± 2 standard deviation scatter bands, while the remaining 8% lie between ± 2 standard deviation scatter bands and ± 3 standard deviation scatter bands.