On the prediction of fatigue life of WAAM-processed Ti-6Al-4V under consideration of manufacturing defects

Purpose There is still a need for a comprehensive investigation into how wire and arc manufactured (WAAM) parts fail under cyclic loading. This study investigates the effect of process-induced defects on the high-cycle fatigue performance of WAAM-processed Ti-6Al-4V with dedicated thermal treatment. Furthermore, the study assesses the applicability of the fatigue life prediction model, which was originally developed and validated for laser beam-welded Ti-6Al-4V joints, to WAAM-fabricated structures. Design/methodology/approach The fatigue life assessment model was adapted to WAAM-fabricated Ti-6Al-4V. This model is based on the NASGRO equation, which considers short crack growth from internal and surface defects, such as lack of fusion defects and pores. The model was used to create artificial Wöhler curves, and the results from stress intensity factor range-decreasing fatigue crack propagation rate tests are compared to the experimental data in the form of a Kitagawa–Takahashi (KT) diagram. Findings The results demonstrate that the model can accurately predict the minimum fatigue life of specimens extracted from WAAM structures. When considering that the crack from internal defects grows in a vacuum-like environment, accurate Wöhler curves are predicted. The experimental data does not follow the expected trends of the KT diagram. Nonetheless, the measured long crack threshold stress intensity factor range produces a suitable estimate of defect severity. Originality/value The study results in a model with which a probabilistic computation of the fatigue life of additively manufactured samples based on the defect size distribution is possible. Furthermore, the KT diagram as a criterion for the assessment of defect severity is evaluated.