A fracture mechanics based semi-probabilistic fatigue lifing approach for additively manufactured Ti-6Al-4V

Volumetric defects in additively manufactured parts cause significant fatigue scatter due to the variations in their size, shape, and location. This study presents a semi-probabilistic framework, combining fracture mechanics and extreme value statistics, for fatigue life estimation in laser powder bed fused Ti-6Al-4V by explicitly incorporating the effect of volumetric defects. Fatigue life estimations were made for the tested specimens and were validated against the experimentally observed fatigue lives. The effect of the volumetric defects' location on fatigue behavior was accounted for by utilizing distinct crack growth constants for cracks initiated from surface and internal defects. The size of the largest defects, expected to be exceeded only once every 100 specimens, for a given probability of failure was estimated using extreme value statistics. The fatigue design curve estimated with this defect size, using the proposed fracture mechanics based lifing approach, was shown to be a better estimate than the one developed using a popular conventional method for fatigue qualification.