Modeling of distributed defects and a proposed fatigue interaction criterion for additively manufactured metal parts

Additively manufactured (AM) metallic components are known to contain distributed geometric discontinuities both internally and at surface. Their effects on fatigue behaviors of AM parts or components need to be better understood for developing cost-effective AM process qualification and part performance certification procedures for safety-critical applications. In this investigation, a rapid fracture mechanic modeling technique is adopted for evaluating the interactions of multiple crack-like defects and their effects on fatigue behaviors of AM test specimens. The parametric study is performed by varying the spacing between defects and the orientations of the defects with respect to the loading direction as well as their proximity to unnotched and notched test specimens. Then, the interactions of defects are examined, and the criterion for treating multiple cracks as a single equivalent crack is presented and compared with existing interaction criteria, e.g., those by ASME XI and BS 7910. Based on the findings of this study, a proposed approach for treating multiple crack-like defects, particularly in highly stressed regions, e.g., near a notch location is presented. Available fatigue test data from unnotched and notched AM specimens have also been analyzed to validate the proposed approach.