Influencing factors on the fatigue strength of selectively laser melted structures

Abstract

This research focusses on influencing factors on the fatigue strength of selectively laser melted (SLM) aluminum structures. One main effect is detected as the surface condition. Therefore, miscellaneous test series involving the as-built surface as well as machined and polished surface topographies are experimentally investigated. In addition, the impact of different post treatments on the fatigue strength is researched. The microstructure of selected samples is studied utilizing SEM images of micrographs whereby microstructural features are assessed. Additionally, the axial residual stresses at the surface of selected specimen are measured using X-Ray diffraction, with the aim to assess influencing factors on the fatigue strength more properly. The fatigue characteristic is evaluated by tension-compression high cycle fatigue tests under a load stress ratio of R=-1. Subsequently to the testing, a fracture surface analysis for each tested specimen is carried out in order to study the failure mechanism and evaluate the fatigue crack-initiating imperfection. The results revealed that for specimens that possess an as-built surface, the high cycle fatigue strength is significantly influenced by surface related characteristics. It is also found that the microstructure affects the fatigue behavior as well.