Influence of surface topology on fatigue of DED-Arc specimens: a NURBS-based 3D-FEA approach

Abstract Directed energy deposition with electric arc sources (DED-Arc) is an additive manufacturing (AM) technology for the production of metal components, particularly in the field of structural steel applications. Its ability to process high-strength low-alloy (HSLA) steels using cost-effective wire feedstock is notable. However, the as-built surface of DED-Arc components is characterised by significant waviness and irregularities due to the nature of the layerwise deposition process. These surface features act as potential stress concentrators and can have a significant effect on fatigue performance. In this study, the influence of surface topology on the fatigue behaviour of DED-Arc-manufactured components of HSLA steels is investigated. Fatigue tests were conducted on specimens in both as-built and machined surface conditions to experimentally quantify the impact of surface waviness. High-resolution 3D scanning and reverse engineering using NURBS-based surface reconstruction were employed to accurately represent real geometries in finite element simulations. Local stress distributions were evaluated to determine fatigue notch factors related to surface waviness. Furthermore, the base material was characterised experimentally by fatigue tests and the results were used in a numerical framework to estimate the fatigue life. Combining the experimental fatigue data with simulation-based notch factor evaluation enabled the development of fatigue life estimation that accounts for manufacturing-induced surface effects. The findings demonstrate the necessity of considering real surface topologies in fatigue assessments and offer a basis for improved design and qualification of AM components.