Impact fatigue behavior of laser metal deposition 316L stainless steel with an automated impact fatigue system based on split Hopkinson bar technique

Abstract

Repeated impact subjecting on the key components of equipment is always characterized by extremely high loading rate loading, while plastic deformation of most metals depends on loading rate. To ensure the reliability and security of these components, it is necessary to understand the loading rate effect on the fatigue performance. In this study, an automated impact fatigue system based on split Hopkinson bar technique was newly developed to investigate the materials’ impact fatigue behavior. Impact fatigue behavior and non-impact fatigue behavior of laser metal deposition 316L stainless steel were analyzed. The fatigue life decreases with the increasing loading rate, implying the significant loading rate dependence. The compression and fracture toughness tests combined with fractography analysis at high and low loading rates were also conducted to reveal the underlying mechanism of the difference between impact and non-impact fatigue life. Finally, microstructure of the laser metal deposition 316L stainless steel after impact and non-impact fatigue was characterized. It can be concluded that the fatigue crack is apt to initiate under impact fatigue due to the high density of dislocation entanglement, while under non-impact fatigue, a large number of twins are beneficial to delay the fatigue crack initiation.