Investigating the impact of printing direction on fatigue behaviour of machined SLM AlSi10Mg through orientation analysis of idealized ellipsoidal defects

The present work deals with the fatigue behaviour of the AlSi10Mg alloy printed by selective laser melting technology. The fatigue performances of machined samples, oriented at 90, 45, and 0 degrees during printing, were assessed through statistical data analysis employing ASTM E739 standard and an innovative extrapolation method at 106 cycles. The fatigue performance of SLM AlSi10Mg resulted worse than the as-cast equivalent, and a significant difference in fatigue behaviour was also observed among the considered printing orientations. For machined samples, the effective defect’s area triggering fatigue was correlated to the mean lifetimes of the batches according to the printing direction. Defects population analysis was conducted through computerized tomography and fracture surface analysis. Assuming ellipsoidal shape of the critical defect, a novel formulation to assess the effect of printing orientation on the fatigue stress limit is proposed. The proposed method allowed the determination of the fatigue stress limit with a maximum deviation of 2.2 % compared to the value extrapolated from experimental data across all printing directions.