Development of an X-ray stress measurement technique for a round corner inside a deep groove

Abstract

A new X-ray stress measuring technique, namely the pseudo-ψ angle-changing method, has been developed to measure the circumferential stress on a round corner located at the bottom of a deep groove such as the tooth root of a gear or the cold-rolled fillet of a crankshaft. This is a multiple-point measurement technique applicable to a curved surface having a uniform stress state. An X-ray path is taken in the plane that does not intersect the sidewalls near the corner. Instead of ψ rotation, the irradiation position is changed along the circumference of the corner with the specimen's attitude against the X-ray path unchanged; diffraction angles at ψ = 0° are measured for different positions of the corner. The position change causes a shift in the diffraction peak since the irradiated area forming a part of the round corner has a different angle of inclination to the incident X-rays. The circumferential stress on the corner is obtained from the relation between the irradiation position and the diffraction angle at ψ = 0°. The validity of this method was verified by applying this technique and the conventional method to model specimens of a rack and a gear having an almost uniform residual stress state introduced by sand blasting, and comparing the stresses measured by the two different methods.