Impact of surface waviness on the XRD residual stress analysis of additive manufactured DED-arc components

Depending on the manufacturing parameters and strategy, components manufactured with DED-Arc sometimes exhibit strong surface topographies, which can be described by the degree of waviness. Additionally, complex residual stress states with gradients in depth but also in lateral direction result from the processing that will affect the service life and must be considered for fatigue analysis. In this contribution two methods of X-ray diffraction (XRD) stress analysis evaluation approaches, the sin²psi method and the cos-alpha method, are employed for residual stress analysis on DED-Arc manufactured components. However, to account for the surface waviness a systematic study is carried out to assess the effect of the surface topography on the results of both the evaluation strategies, since it is well-known, that surface waviness and curved surfaces measured based on the cos-alpha method can lead to spurious out-of-plane shear stresses. For this reason, reference samples are manufactured having a homogeneous microstructure and a defined surface waviness comparable to typical DED-Arc manufactured parts, to be able to separate the surface effect. Moreover, a comparison on real DED-arc manufactured specimens are performed. By this systematic study, the influence of surface waviness on residual stress analysis by XRD using different evaluation approaches is quantified.