Accurate comparison of optical and X-ray computed tomography surface texture measurements on additively manufactured test specimens to improve the accuracy of fatigue life predictions

This paper introduces a novel approach to compare surface texture measurements obtained from computed tomography (CT) and optical profilometry (OP) on Ti6Al4V additively manufactured fatigue specimens, aimed at enhancing fatigue life predictions. Traditional alignment methods, often requiring fiducials or markers on the part, can alter the specimen's geometry or surface properties. To address this issue, we developed a measuring setup that allows precise data alignment without any alterations to the surface. Surface texture was analysed over the entire cylindrical gauge length using standardised roughness parameters, comparing CT and optical profilometry data to identify areas of agreement and discrepancy while identifying potential sites of crack initiation. This multi-instrument measurement approach will provide a deeper understanding and characterisation of surface pits that may undermine fatigue life and it lays the foundation for improving life prediction accuracy in as-built additive manufacturing surfaces. Surface metrology, optical profilometry, computed tomography, multi-instrument surface characterisation, additive manufacturing