Investigation of the anisotropic fatigue behavior of additively manufactured structures made of AISI 316L with short-time procedures PhyBaLLIT and PhyBaLCHT

Abstract To exploit the high potential of additive manufacturing (AM) technology for production of safety relevant structural components, it is indispensable to get a sound knowledge about the fatigue behavior of additively manufactured materials. However, fatigue investigations are time and material consuming, leading to high costs for fatigue validation of AM materials. To reduce this effort, in this research work the short-time procedures PhyBaLCHT (CHT: cyclic hardness test), based on cyclic indentation testing, and PhyBaLLIT (physically based lifetime calculation; LIT: load increase test), based on load increase tests (LITs) are used to comprehensively characterize the fatigue behavior of selectively laser melted specimens made of austenitic stainless steel AISI 316L in three different building directions. The different building directions lead to layer planes perpendicular (SLM-V), in 45° direction (SLM-45) and parallel (SLM-H) to the loading direction. In addition to the short-time procedures, several constant amplitude tests (CATs) were performed to validate the results. The results of CATs showed only slight differences in the fatigue behavior of SLM specimens, which correlates well with the results of LITs. Furthermore, the results of CATs demonstrate a high influence of the microstructural defects i.e. pores on the fatigue behavior and different defect tolerances depending on the building direction. The vertical building direction lead to the highest defect tolerance, which is proved by the results of PhyBaLCHT. The S-Nf curves, calculated by the PhyBaLLIT approach, are in good accordance to the CATs and hence, can describe the characteristics of the fatigue properties of the different orientations with good accuracy. Consequently, the influence of different building directions on the fatigue behavior of the SLM specimens could be determined efficiently with the presented short-time procedures.