Fatigue life estimation of additively manufactured Ti-6Al-4V: Sensitivity, scatter and defect description in Damage-tolerant models

Abstract

Damage-tolerant models for fatigue life estimation rely on fracture mechanics principles to model fatigue crack initiation and growth. In Laser-Based Powder Bed Fusion (LPBF) produced Ti-6Al-4V defect populations present non-uniform in size, shape, and location within components. Considering defect populations in a statistical nature offers one method to characterise defects to be included in fatigue life modelling for AM parts. In this study a novel numerical fatigue life model is built upon which the sensitivity to input parameters, short crack growth mechanics, defect morphology and location for LPBF-produced Ti-6Al-4V is established. Furthermore, we introduce the potential for multiple crack initiation sites and crack interaction. Fatigue strength is shown to be more sensitive to selected threshold parameters and short crack growth mechanics. Furthermore, the introduction of multiple crack initiations and interaction results in distributions of fatigue strength estimates sensitive to defect number, illustrating the importance of its inclusion as a source of fatigue scatter in LPBF produced Ti-6Al-4V parts. Overall, this study establishes areas of nuance and criticality required in the design and modelling of fatigue life unique to AM produced components.