Numerical investigation of the effect of defect population on the fatigue strength anisotropy of alloys fabricated by L-PBF

This study investigates the impact of defects on the fatigue strength anisotropy of Ti-6Al-4V alloy fabricated by Laser Powder Bed Fusion (L-PBF). Finite element simulations are performed to analyze two defect populations, lack of fusion (LoF) defects and gas pores, under multiaxial proportional loading conditions. Results demonstrate that fatigue strength is highly sensitive to the polar angle θ representing the defect orientation with respect to the mechanical loading and is primarily influenced by defect morphology, transitioning from low sphericity (LoF defects) to high sphericity (gas pores). The anisotropic behavior is particularly pronounced under tensile loading, where the morphology of LoF defects and loading directions exhibit a notable influence. Shear loading exhibits reduced sensitivity to these factors. The proposed statistical methodology allow to determine the fatigue strength anysotropy for any multiaxial loading configuration and defect population. The numerically obtained fatigue strength anisotropy matches the one obtained experimentally in the literature and non-local analysis smoothens the fatigue strength surface response, leading to a reduction in the anisotropic factor ( λ ). • Fatigue strength anisotropy depends on defect morphology and load direction. • LoF defects show higher anisotropy than gas pores due to tortuous shape. • Non-local analysis lowers both anisotropy and variability in fatigue strength. • Anisotropy is highest in tension and lowest in shear under fully reversed load.