As-built Ti-6Al-4V thin parts were manufactured in three different orientations using EBM and characterized by laboratory X-ray tomography. Fatigue tests were performed. The comparison with results for machined samples from the literature showed a large reduction of fatigue strength. SEM observations of the fracture surfaces showed that surface defects which were identified as notch-like defects on tomographic images caused the failure. Their impact on fatigue results was rationalized by Kitagawa-Takahashi diagrams. A build orientation impact on the fatigue properties was observed and linked to its effect on defects distributions and crack growth. The limits of roughness measurements were also discussed.

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The fatigue properties of lattice structures produced by S-EBM are investigated. Fatigue failure is shown to be gradual, fostering the concept of grace period, defined as the number of cycles lived by the lattice structure after the failure of the first strut. A numerical framework based on the cascading failure of struts is proposed, relying on a damage accumulation law. Each strut is assigned a radius as well as an S-N curve, which both depend on the manufacturing conditions. Through statistical analyses, we demonstrate that the model can correctly predict the grace period and the fatigue life of experimental specimens.

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