Defect-based multiaxial fatigue life prediction of L-PBF additive manufactured metals

Fatigue cracks in additively manufactured (AM) components typically initiate from critical defects such as gas porosities and lack of fusion defects. In addition, such components are often subjected to multiaxial stresses at fatigue critical locations due to complex geometry and/or multiaxial loads. In this work, a fracture mechanics framework based on defects and their characteristics was used for multiaxial fatigue life prediction of laser-based powder bed fusion (L-PBF) fabricated Ti-6Al-4V and 17-4 PH specimens as illustrative examples. Modes I and II and mixed-mode small crack growth were considered in the predictions based on the experimentally observed damage mechanisms, depending on the metal, fabrication process, and post-process treatment conditions. Implications of initial defects characteristics under multiaxial loading and the effect of roughness-induced closure in mixed-mode crack growth are also discussed