Fatigue crack initiation in additively manufactured maraging steel: A statistical insight

High cycle fatigue tests were performed on three different-sized, laser powder bed fusion (L-PBF) fabricated MS1 maraging steel specimens at room temperature and at a stress ratio of -1, with qualitative and statistical investigation of the defect size and shape on the fatigue lives. The mechanical and fatigue properties were not much affected by the change in gauge volumes (128, 250, 432 mm3) investigated in this study owing to the similar distribution of the internal porosities. Interestingly, the manufacturing defects were mostly present near the free surface of the L-PBF fabricated parts instead of being uniformly distributed within the control volume. A significant scatter in the fatigue life data was attributed to the geometric parameters: shape, size, and location of the crack-initiating defects within the fractured specimens. The ratio of the defects' size to their location with respect to the free surface was found to dictate the total fatigue life. The probabilistic S-N curves based on two popular models: the Weibull model and the St & uuml;ssi model, were plotted in addition to the conventional Murakami's model to predict the fatigue life and strength. Conclusively, the St & uuml;ssi Model appeared to generate a safer fatigue design curve with the broadest bandwidth covering the experimentally observed uncertainties. The obtained results showed a good correlation with the experimental results and established the reliability of the research.