The experimental determination of residual stress becomes more complicated with increasing complexity of the structures investigated. Unlike the conventional and most of the additive manufacturing (AM) fabrication techniques, laser powder bed fusion (PBF-LB) allows the production of complex structures without any additional manufacturing step. However, due to the extremely localized melting and solidification, internal stress-induced deformation and cracks are often observed. In the best case, significant residual stress is retained in the final structures as a footprint of the internal stress during manufacturing.

Here we report solutions to the most prevalent challenges when dealing with the diffraction-based determination of residual stress in AM structures, in particular the choice of the correct diffraction elastic constants. We show that for Nickel-based alloys, the diffraction elastic constants of AM material significantly deviate from their conventional counterparts [1]. Furthermore, measurement strategies to overcome the hurdles appearing when applying diffraction-based techniques to complex-shaped lattice structures are presented: a) proper sample alignment within the beam, b) the proper determination of the residual stress field in a representative part of the structure (i.e., with an engineering meaning). Beyond the principal stress magnitude, the principal direcions of residual stress are discussed for different geometries and scan strategies, as they are relevent for failure criteria [2, 3].

We show that the RS in the lattice struts can be considered to be uniaxial and to follow the orientation of the strut, while the RS in the lattice knots is more hydrostatic. Additionally, we show that strain measurements in at least seven independent directions are necessary for the correct estimation of the principal stress directions. The measurement directions should be chosen according to the sample geometry and to an informed choice on the possible strain field (i.e., reflecting the scan strategy) [3].

We finally show that if the most prominent direction is not measured, the error in the calculated stress magnitude increases in such a manner that no reliable assessment of RS state can be made. [2]

[1] J. Schröder, T. Mishurova, T. Fritsch, I. Serrano-Munoz, A. Evans, M. Sprengel, M. Klaus, C. Genzel, J. Schneider, G. Bruno. Mater. Sci. Eng. A, 2021, 805, 140555.

[2] T.Fritsch, M.Sprengel, A.Evans, L.Farahbod-Sternahl, R.Saliwan-Neumann, M.Hofmann, G.Bruno. J. Appl. Cryst. 2021, 54, 228–236.

[3] J. Schröder, A. Evans, V. Luzin, G. Abreu Faria, S. Degener, E. Polatidis, J. Capek, A. Kromm, G. Dovzhenko, G.Bruno. J. Appl. Cryst. 2023, 56, 1076-1090.