Residual Stress Induced Fretting Fatigue during Fatigue Testing for Materials Produced by Laser Powder Bed Fusion Process

Fretting fatigue was observed in standard cylindrical fatigue samples at the regions in contact with the grips of the test frames during fatigue testing for AlSi10Mg aluminum alloy produced by laser powder bed fusion process (L-PBF). The failure of the fatigue sample grips occurs much earlier than the failure of the gauge section. This results in a damaged sample and the sample cannot be reused to continue the test. This type of failure is rarely seen in materials produced by traditional manufacturing processes. In this study, X-ray residual stress analysis was performed to understand the cause of failure for L-PBF AlSi10Mg with the as-built surface condition. The result indicates that the fretting fatigue failure was caused by the strong tensile residual stress in the as-built state combining with the fretting wear between the sample and the grip. A few potential solutions to avoid the fretting fatigue failure were investigated. The results show that stress relieving is the most effective method. However, this is not always feasible as it changes the mechanical properties and microstructure, as well as the fatigue properties. If the fatigue properties in the as-built state are desired, the sample grip should be made with a larger diameter and a significant amount of material needs to be removed to obtain the final diameter.