Fatigue assessment of 316L DED-arc structures considering individual surface topography

Abstract The surface topography of parts and components manufactured by direct energy deposition arc (DED-arc) based on additive manufacturing is crucial for fatigue behavior. In this study, DED-arc specimens made of AISI 316L are characterized according to their mechanical properties and surface topography (waviness). The specimen surface was digitized by 3D scanning. Fatigue tests were performed in as-printed condition and milled condition (flat surface). The crack initiation locations of each individual specimen were determined to correlate individual geometry and failure location. The specimens made of 316L showed a significant waviness of up to 1.4 mm. The fatigue tests were evaluated with different concepts: the nominal stress approach based on different definitions of the cross sections, as well as local approaches like the maximum stress (notch stress), critical distance, or stress gradient approach. The scatter in the S–N curves was significantly reduced by using all three local approaches, with the lowest scatter observed using the maximum stress approach. The fatigue life was assessed by linear elastic fracture mechanics (LEFM) using best practice input parameters based on the fatigue life assessment of welded joints. By LEFM, conservative fatigue life values could be reached according to the experiments, especially for low load levels. A combination of local approaches with LEFM leads to a very good agreement in the investigated case.