Fatigue strength and life assessment of L-PBF 316L stainless steel showing process and corrosion related defects

The present work focuses on the modelling of the fatigue behaviour of a 316L produced by laser powder bed fusion containing various defect populations : Lacks of fusion, corrosion pits and one electric discharge machined hemispherical defect. As shown in previous experimental studies, the crack leading up to failure systematically initiated on a single surface defect. The nature and morphology of the critical defect didn’t show any influence on the fatigue strength, and only its size seemed to matter. To take into account the critical defect size, models based on linear elastic fracture mechanics were implemented and identified. A modified Paris propagation law was used to model the short crack regime. This approach was used to predict S-N curve domains based on critical defects size range. • Original fatigue tests of a L-PBF 316L SS with different types of defects (pores, corrosion pits, artificial defects) and specimens geometries were carried out. • The effect of the microstructure of the L-PBF material was discussed and compared to the wrought one. The microstructure may affect the fatigue strength of metallic matrix. • The critical defect size seems to be the first order parameter driving the specimen fatigue strength. The defect shape or type did not show any influence on the fatigue limit. • Linear Elastic Fracture mechanics models were implemented to take into account the effect defect size for fatigue life predictions. • S-N curve domains were defined for the different critical defect populations. These domains were in good agreement with the experimental results.