抄録
The authors have carried out fundamental studies on the stress measurement by means of X-rays for the purpose of extending their application to practical engineering problems. One of them is for the improvement of the accuracy of stress measurement. In place of taking the shift of the peak position of diffraction profile for measuring lattice strain, the authors had previously proposed a new method of separation of Kα1 component from Kα doublet using Fourier analysis for the improvement of accuracy of X-ray stress measurement for a sample with a broad diffraction profile. This method is characterized as being applicable to the measurement of peak position of diffraction profiles with various shapes including broad ones.
However, the numerical calculation of this method is exceedingly complicated because the Fourier analysis is introduced in the measuring process. For this reason, a convenient method has been devised for the measurement of stress, which is by measuring the center of gravity of Kα doublet without use of Fourier series, keeping on the advantages of above mentioned method, was proposed. The calculation of the center of gravity can be easily and quickly performed as compared with the previous case.
Moreover the effect of Lorentz polarization and the absorption factors on the measured stress should be also discussed in the case of the measuring sample which has a large amount of residual stress and shows a broad diffraction profile. From this point of view, the authors previously discussed the effect of both factors (LPA factor) and reported that these effects on the measured stress are remarkable when the specimen has a broad diffraction profile and a large amount of residual stress. However, the quantitative effect of LPA factor on the stress value should be known because the calculation at each measurement are very complicated.
In the present study, the authors discussed on the quantitative effect of LPA factor on the stress value by using the half-value breadth of Kα doublet as a parameter.
The following assumptions were used; (1) The intensity distribution curves φ1(x)LPA and φ2(x)LPA, which are corrected by LPA factor, obtained from Kα1 and Kα2 radiations, respectively, are represented by Gaussian distribution curves. (2) The following relation holds between φ1(x)LPA and φ2(x)LPA.
Φ(x)LPA=φ1(x)LPA+φ2(x)LPA, φ2(x)LPA=kφ1(x/Δx)LPA,
where k is a constant, Δx is the distance between the peak position of the intensity curves diffracted from Kα1 and Kα2 radiations, and Φ(x)LPA is the intensity curve which is corrected Φ(x) diffraction curve by using LPA factor.
If the intensity distribution curve φ1(x)LPA, the value of peak position and the half-value breadth are given, Φ(x) curve can be composed. The relation between the gravitation center of Φ(x) and the peak position of φ1(x)LPA, and between the half-value breadths of Φ(x) and φ1(x)LPA are obtained. Furthermore, when the stress value σ1.LPA measured from φ1(x)LPA is given, Bragg's angle (peak position of φ1(x)LPA) can be calculated from the fundamental equation of stress measurement by means of X-rays and Bragg's equation. Therefore, the gravitation center of Φ(x) is calculated and then stress σ determined from Φ(x) is obtained.
