Fatigue-Life Prediction of Additively Manufactured Material: Effects of Defect Spacing and Multi-Site Damage

Abstract

Fatigue-life prediction of additively manufactured metals is challenging due to the random distribution of process-induced defects, whose proximity can significantly influence crack initiation and propagation, and whose multiplicity can promote multi-site damage. Prediction approaches based on single-crack growth often overestimate fatigue life by neglecting defect interactions and multi-site crack propagation, particularly in low cycle fatigue and mid-life regimes, where crack coalescence and stress field interactions play a crucial role. This study integrates small- and large-crack growth test data with defect characteristics, including size and spacing obtained from X-ray computed tomography, to estimate the fatigue life of Ti-6Al-4V fabricated via laser directed energy deposition. The plasticity-induced crack closure model, FASTRAN, was employed to simulate crack propagation and compare single-crack and multi-crack approaches in fatigue-life prediction. The multi-site damage approach, which explicitly accounts for defect spatial distribution through nearest neighbor distance analysis, significantly improves fatigue-life predictions in low cycle fatigue and mid-life regimes, demonstrating strong agreement with experimental data.