Abstract
In sin2, ψ method used in X-ray stress measurement, the stress is analysed on the basis of information about the strain obtained from the diffracted beam in the specified direction on Debye-Scherrer ring. Any diffracted beam in other directions on the same Debye-Scherrer ring can also give information about the strain on normal to diffraction plane. Therefore, it is possible to estimate the stress more accurately, since any information on Debye-Scherrer ring can be adopted to φ-sin2ψ method suggested by the authors. In order to improve the accuracy of stress measured at such a portion where the direction of incident X-ray is confined, the authors examine to evaluate the stress by φ-sin2ψ method on the basis of the information about strains obtained from diffracted beam in various directions on Debye-Scherrer ring. Moreover, the accuracy of residual stress on fillet welded joint measured by φ-sin2ψ method is also discussed in this report. The results obtained are summarized as follows:
(1) In measurement of a diffraction angle by counter method, the direction (Φ, Ψ) of normal to a diffraction plane in an arbitrary direction on a Debye-Scherrer ring is given by following equations,
sin2Ψ = 1-(cosψ0cosη0-sinψ0sinη0cosω)2
Φ=tan-1{ sinΦ0(sinψ0cosη0+cosψ0sinη0cosω)+cosφ0sinη0sinω/cosΦ0(sinψ0cosη0+cosψ0sinη0cosω)-sinφ0sinη0sinω }
where Φ0 and ψ0 show the directions of incident X-ray, ω is the rotating angle of the plane of counter scanning about the axis of incident X-ray and η0 the complement of diffraction angle on strain-free crystal. Therefore the information about the strain required to stress analysis in φ-sin2ψ method consists of the direction of normal to diffraction plane given by above equations and the measured diffraction angle.
(2) The stresses, which are estimated by φ-sin2ψ method on the basis of information about the strain obtained from diffraction beam in arbitrary directions on Debye-Scherrer ring, are accurate enough for practice.
(3) In a fillet weld, since the domain of direction of adopted normal to diffraction planes with measurable diffraction angle is larger in the case where the direction of the plane of counter scanning is variable than in the case of the fixed plane of counter scanning, it is possible to estimate more accurate value of residual stresses on the basis of the information about strains obtained from the larger domain.
