2回どり写真法によるX線応力測定

抄録

The X-ray radiation area is required to be small so as to measure the X-ray residual stresses of rolling surface of ball bearing, balls and rollers. In this case, photo method is more effective than the counter method.
Quenched bearing steel presents greatly diffused diffraction pattern, however, so that it is difficult to measure the X-ray residual stresses with high reliability. In order to improve the reliability of X-ray stress measurement for accuracy in the photo method, we have investigated on factors of the error in the photo method. In the photo method, remarkable factors which reduce reliability for accuracy exist in the X-ray photographic technique.
One of them is an error induced during the determination of the center of diffraction ring. Another problem is difficulties of determining representative position from intensity curve for its broadening.
On the correlation of the X-ray and the mechanical stress and reproducibility of the X-ray stress, we investigated the effects of three methods in which the center of diffraction ring is to be determined. They are as follows:
(1) a method in which the center of punch hall is assumed to be the center of diffraction ring.
(2) a method in which tin powder is used as standard specimen.
(3) a new method invented by the authors.
A new method that the same half-round of diffraction ring is twice exposed on a film rotated at the angle of 180 degrees between the first exposure and the second, named "Twice Exposure Photographic Method", has great effect on improving the reliability of X-ray stress measurement.
It shows only ±3kg/mm² scattering in reproducibility and correspondence to the mechanical stress, although other two methods shows ±8-15kg/mm² in measuring quenched bearing steel.
Considering these results, two factors previously mentioned are really important and are eliminated by our new "Twice Exposure Method".