In the realm of additive manufacturing (AM), the microstructure, defects, and surface roughness play pivotal roles in determining the fatigue performance of materials intended for engineering applications. This study employs modern testing strategies and advanced measurement techniques to precisely monitor the impact of process-induced characteristics on fatigue behavior.

Intermittent fatigue testing has been employed to unveil the intricate interaction between microstructure, local porosity, and fatigue crack initiation, particularly extending into the very high cycle fatigue (VHCF) region. The investigation spans across materials such as 316L, AlSi, TiAl, and Ni alloys, wherein the effects of defects, building direction, and stress ratio on fatigue evolution have been examined.

The correlation between fatigue strength and material properties, specifically hardness, has been established. Additionally, the effective defect or pore size relative to the load direction has been analyzed using the Murakami-Noguchi concept. Through an elastic-plastic modification using the J-integral proposed by Heitmann, the study has successfully demonstrated the influence of microstructure on cyclic stress-strain behavior and fatigue damage tolerance.

The findings of this research showcase promising avenues for enhancing fatigue lifetime and damage tolerance by establishing comprehensive structure-property relationships. These relationships can be seamlessly integrated into uniform fatigue damage tolerance approaches. The implications of this study not only contribute to a deeper understanding of the fatigue mechanisms in AM processes but also offer practical insights for optimizing material performance in engineering applications. The results pave the way for the development of robust and reliable additive manufacturing processes with improved fatigue characteristics.