The standard method for X-ray stress measurement was recently established by the Committee on Mechanical Behaviour of Material, Japan. Thus, the stress determination by means of X-rays will be more widely used in the future at laboratories or factories on the basis of this standard, and the automatic measurement will be required as the numbers of measurement increase.
In“the standard method”, the diffraction profile is recorded as the intensity-angle curve by means of a counter. The peak position of the profile, 2θ, is graphically determined by the half-value breadth method, and the stress σ is then calculated from the gradient of 2θ-sin2ψ diagram.
In this paper presented is a half-value breadth method by digital computation to determine the peak position of profile, which is suitable for the automatic measurement of X-ray stress. Several examples are also shown. In this method, the diffraction intensities are converted to the digital values at equal intervals in the diffraction angle. The background line of profile is calculated from the data of both ends of the profile on the basis of correlation coefficient of linear regression. The half-value breadth line is then drawn parallel to the background line. The values at the intersections between the half-value breadth line and the profile are calculated approximately by the simultaneous equations, and the midpoint between two intersections is defined as the peak position.
The measurements of stress were performed by the standard method and this computation method on several carbon steel specimens. The measured values of peak position of profiles by these two methods almost agreed each other, and the difference of stresses by these methods was as small as under 1kg/mm2.
