Contribution of the introduction of artificial defects by additive manufacturing to the determination of the Kitagawa diagram of Al-Si alloys

Abstract

Despite the continuous progress in the additive manufacturing (AM) technologies to improve the quality of the produced parts, the presence of defects induced by the process remains a critical issue for the design of industrial components with respect to fatigue damage. Analytical models such as Kitagawa diagrams represent easy to use tools to predict fatigue strength accounting for the detrimental influence of the defects. They are therefore of great interest from an industrial point of view. The aim of the present work is to evaluate whether artificial defects obtained by placing holes directly into the CAD files of fatigue specimens can be used to establish Kitagawa diagrams, despite some differences in terms of shapes and morphologies between the natural and artificial defects. Two artificial defect geometries with a similar size were studied. For each of these geometries, the experimental fatigue strengths and the real sizes of the critical defects measured from the fracture surfaces were used to determine the parameters of the El-Haddad model. For one of the geometries, the obtained model was able to predict the fatigue strength corresponding to the natural defects, and the associated parameters were found consistent with the literature. The fatigue tests results also highlighted the influence of the defect shape.