Multiaxial fatigue behavior and modeling for additive manufactured Ti-6Al-4V: The effect of surface texture

The rough surface texture of unmachined specimens produced by the laser powder bed fusion (L-PBF) technique can significantly reduce their fatigue strength. Accurate measurement of surface topography is essential for obtaining reliable surface roughness parameters to enable quantitative comparisons and fatigue life estimations. A hybrid surface roughness parameter, previously proposed for uniaxial fatigue scenarios, linking surface texture with the fatigue strength of L-PBF materials, has been adopted to estimate the effect of surface texture on the multiaxial fatigue behavior of L-PBF Ti-6Al-4V alloy. Surface topographies are thoroughly measured using an optical microscope and X-ray computed tomography, and the outcomes of the two techniques are compared. Multiaxial fatigue results are analyzed using three different fatigue models. The surface texture-based fatigue life estimation approach is then combined with these three models to estimate the fatigue strength of different surface texture conditions under multiaxial loading. The results indicate that while the surface texture-based fatigue life estimation approach was originally developed for uniaxial loads, it could be extended to torsion as well as combined axial-torsion stress states. It was also found that the approach works only when the appropriate multiaxial fatigue life estimation model, consistent with the failure mechanism of the material, is utilized.