• Klaus, M.; Genzel, C.: Reassessment of evaluation methods for the analysis of near-surface residual stress fields using energy-dispersive diffraction. Journal of Applied Crystallography 52 (2019), p. 94-105

10.1107/S1600576718018095

Abstract:
In this paper two evaluation methods for X-ray stress analysis by means of energy-dispersive diffraction are reassessed which are based on the sin^2⁡ψ – measuring technique. Advantage is taken of the fact that the d_ψ^hkl-sin^2⁡ψ data obtained for the individual diffraction lines E^hkl not only contain information about the depth and orientation dependence of the residual stresses, but also reflect the single crystal elastic anisotropy of the material. With simulated examples it is demonstrated that even steep residual stress gradients can be determined from sin^2⁡ψ-measurements, that were performed up to maximum tilt angles of about 45°, since the d_ψ^hkl-sin^2⁡ψ distributions remain almost linear within this ψ – range. This leads to a significant reduction of the measuring effort and at the same time also makes more complex component geometries accessible for X-ray stress analysis. Applying the modified multi-wavelength plot method for data analysis it turns out that a plot of the stress data obtained for each reflection hkl by linear regression versus the maximum information depth τ_(ψ=0)^hkl results in a discrete depth distribution which coincides with the actual LAPLACE space stress depth profile σ(τ). The sensitivity of the residual stress depth profiles σ(τ_(ψ=0)^hkl ) to the diffraction elastic constants 1/2 S_2^hkl used in the sin^2⁡ψ – analysis can be exploited to refine the grain interaction model itself. With respect to the universal plot method the stress factors F_ij which reflect the materials anisotropy on both, the microscopic scale (single crystal elastic anisotropy) and the macroscopic scale (anisotropy of the residual stress state) are used as ‘driving forces’ to refine the strain-free lattice parameter a_0 during the evaluation procedure.