2017 年 66 巻 7 号 p. 488-494
The investigation was made on the phenomena observed in the X-ray stress measurement on a curved surface by the cos α method. Numerical analysis was performed simulating the cos α method for the circumferential stress and the axial stress on a cylindrical surface. The X-ray residual stress measurements by the cos α method and the sin2ψ method were carried out respectively for the blasted surface of round steel bars with various diameters. It was found that the debye ring turned oval and the slope of cos α diagram decreased as the ratio of the X-ray beam size to the bar diameter increased, i.e. the magnitude of the measured stress was smaller than that of actual one. These tendencies were remarkable in the circumferential stress measurement. With respect to the relation between the X-ray beam size and the measured value of stress, the difference between the cos α method and the sin2ψ method was found to be small. The measurement error due to a cylindrical surface was negligible when the X-ray beam size was less than 1/3 of the diameter.