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Reassessment of evaluation methods for the analysis of near-surface residual stress fields using energy-dispersive diffraction

2019; Wiley; Volume: 52; Issue: 1 Linguagem: Inglês

10.1107/s1600576718018095

1600-5767

Manuela Klaus, Christoph Genzel,

Fatigue and fracture mechanics

In this paper two evaluation methods for X-ray stress analysis by means of energy-dispersive diffraction are reassessed. Both 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 could be determined from sin 2 ψ measurements that are 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 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 ½ 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 material's 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.