Technical parts and components often have a highly inhomogeneous surface topography in form of notches, grooves or strong local curvatures (e.g. gear wheels, springs), which place very high demands on X-ray stress analysis (XSA). Since XSA is based on the precise measurement of diffraction line positions and their shifts due to the material inherent (i.e. residual) stresses [1,2], the surface topography of the investigated sample plays an important role for measurements performed in reflection geometry. This is because the depth range below the surface, from which the information of the diffraction signal originates, is limited to a few tens to a few hundred micrometers, depending on the photon energy and absorption of the material. In [3] the authors have identified four effects that cause diffraction line shifts in such cases and must therefore be taken into account in the evaluation. The shifts originate from (i) the rotation of the local stress reference system, (ii) its translation from the diffractometer center, (iii) absorption and (iv) partial shadowing and/or screening of the X-ray beam.
The work presented aims at a systematic study of the rotation effect (psi-missetting) [4] by XSA using energy and angle dispersive diffraction performed on a ferritic steel sample with a well-defined surface topography. It is characterized by three grooves that have the same nominal diameter but have been milled to different depths into the flat surface. Modifications of the fundamental equation of XSA are proposed that allow to correct the hoop and longitudinal stresses obtained from sin2psi-measurements on samples featuring an inhomogeneous surface topography.

References
[1] I. C. Noyan, J. B. Cohen; Residual Stress Measurement by Diffraction and Interpretation, New York: Springer 1987.
[2] V. Hauk; Structural and Residual Stress Analysis by Nondestructive Methods, Amsterdam: Elsevier 1997.
[3] M. Francois, J. M. Sprauel, J. L. Lebrun; in Proc. 3rd International Conference on Residual Stresses (ICRS3), Tokushima, Japan, CRC Press 1992, pp. 933 – 938.
[4] M. Francois, B. Dionnet, J. M. Sprauel, F. Nardou; J. Appl. Cryst. 1995 28, pp. 761 - 767.