The effect of preload on the fatigue strength of additively manufactured 316L stainless steel

Sammanfattning: In this thesis an investigation of the effect of preload on the fatigue behaviour of additively manufactured (AM) 316L stainless steel parts with less than 5 % porosity, for both horizontal and vertical build direction, is presented. The specimens used were manufactured by selective laser melting (SLM) and cut by EDM. Preloads at two different magnitudes were used, below and above the yield strength of the material, and fatigue tests were performed on the specimens with and without the preloads. In addition, microstructural analysis was carried out in order to illustrate/quantify the defects and to realize the corresponding effect of the preload by use of white light interferometry (WLI), SEM and FEM modeling. It was found that the fatigue life and the fatigue limit clearly increase with increasing the preloads in both build directions, although the preload significance might be varied for different directions. This was attributed to the imposed compressive residual stresses and blunting of sharp defects after preloading.