Influence of the Peening Intensity on the Fatigue Behavior of Shot Peened Titanium Components

Although mechanical surface treatments are commonly used in engineering practice for their beneficial effect on fatigue life, little quantitative data are available from published literature. This paper presents the first results of a long-term research program that aims to develop quantitative design guidelines for the influence of mechanical surface treatments on the fatigue life of structural lightweight components. To gain a detailed understanding of the effects of mechanical surface treatments on surface roughness, residual stress distribution, and resulting fatigue strength, extensive experimental work as well as accompanying fracture analyses have been performed. Four-point rotating bending tests and alternating torsional tests were performed on a Ti-6Al-4V titanium alloy. Both smooth and notched specimen geometries were investigated. The heat-treated and machined specimens were subjected to a shot peening process with varying shot intensities within the recommendations of the MIL-S-13165C and MIL-P-81985 specifications. It was observed that shot peening can result in both an improvement as well as a deterioration in fatigue strength, depending on the shot peening intensity and the type of loading. For the assessment of the fatigue failure mechanisms, detailed investigations of the surface layer were included in the research program.