Predicting the fatigue performance of an additively manufactured Ti-6Al-4V component from witness coupon behavior

Abstract

The relationship between the reported fatigue performance of an aerospace laser powder bed fused (L-PBF) Ti-6Al-4V component and witness coupons is examined. Traditional deterministic fatigue life models calibrated to witness coupon fatigue data are found capable of predicting the trend in median component fatigue performance, motivating deeper analysis with a probabilistic fatigue life model. A weakest link model is formulated that is applicable to heterogeneous stress states and the transition in failure mode that occurs in Ti-6Al-4V. After calibrating to the witness coupon data, the model is found capable of predicting key trends in the reported component data. After a discussion of the predicted variability and uncertainty, the model is utilized to illuminate how variations in crack initiation site density, e.g. build defects, might impact fatigue performance at the coupon and component level. By comparing to additional literature data, a wide range of sensitivity to initiation site density is illustrated, and subsequently explained via an approximate expression of the model that shows a dependence of sensitivity on the nature of the material and its initiation sites, as well as the level of inspection that is performed.