Surface roughness effects on the fatigue strength of additively manufactured Ti-6Al-4V

Additive manufacturing has become an increasingly popular advanced manufacturing technique, however, many questions concerning the reliability of parts fabricated by methods such as laser powder bed fusion must be addressed. In this research, the effect of surface roughness and size is investigated by designing various additively manufactured Ti-6Al-4V specimen geometries. These as-built specimens were designed to specifically determine the effect of surface area and part diameter on the fatigue behavior of specimens fabricated diagonally from the substrate. Results indicate that the fatigue behavior is more sensitive to part diameter than surface area. Parts with diameters of 4.90 mm or less showed higher surface roughness on the down-skin surface. This variation diminished, however, for specimens with diameters larger than 4.90 mm. Additionally, as part diameter decreased, the difference between the load-bearing and nominal stress amplitudes, caused by surface roughness, increased, resulting in significant scatter in the high cycle fatigue data.