Nondestructive residual stress depth profile analysis at the inner surface of small boreholes using energy-dispersive diffraction under laboratory conditions.

Energy-dispersive diffraction under both laboratory and synchrotron conditions was applied to study the hoop stress in the near-surface region of the inner wall of boreholes with a small diameter of 2 mm. By use of different X-ray beam cross sections for the sinψ measurements, it is demonstrated that the borehole-to-beam-diameter ratio must be considered in the evaluation. A beam cross section which is comparable to the borehole diameter reduces the slope of the -sinψ distributions and thus invalidates the result of stress analysis. A quantitative relationship is applied, which allows the results obtained under the above conditions to be scaled so that they reflect the actual residual stress state at the measurement position. Owing to the small diffraction angles, energy-dispersive diffraction proves to be the only suitable experimental technique that allows a nondestructive and depth-resolved analysis of the hoop stress component at the inner surface of boreholes with a large length-to-diameter ratio.