Influence of mean stress and building orientation on the fatigue properties of sub-unital thin-strut miniaturized Ti6Al4V specimens additively manufactured via Laser-Powder Bed Fusion

Fatigue is a complex, localized phenomenon affecting lattice structures at the level of struts and junctions. This study examines the fatigue properties of Laser-Powder Bed Fusion (L-PBF) Ti6Al4V miniaturized strut-like specimens, printed in four distinct building orientations (0 degrees, 15 degrees, 45 degrees, 90 degrees), and subjected to four stress ratios (R = 0.1, R = -1, R = -4, R = 10). Experimental data, summarized in Haigh diagrams, align well with predictions from the SWT and Walker methods. Notably, the dependency on mean stress diminishes as the building angle increases, attributed to progressively lower surface roughness which primarily drive failure at R = 0.1 and R = -1. In contrast, vertical specimens at R = -4 display a pronounced susceptibility to sub-surface defects affecting their fatigue strength, a finding corroborated by CT scan analyses. Additionally, the influence of buckling on fatigue performance is investigated and incorporated into the Haigh diagrams. These findings can contribute to a more informed design of L-PBF Ti6Al4V lattice structures against fatigue.