X-ray residual stress measurement on mechanical components with high curvature

In this paper we deal with the definition of an appropriate X-ray diffraction procedure for residual stress determination on samples with high curvature radius. We choose as the application high-strength hot worked coil springs for car suspensions (wire diameterd=12 mm). Different methods of X-ray measurement area limitation are compared, taking into account the measurement errors, for the determination of stress in one and in three directions. After the identification of the irradiated area limits for plane samples, further limits are identified due to the sample curvature (torsion bar). We describe loading devices purposely designed, constructed and calibrated. In each case, the sample is loaded so that the stress state is determined at the same time both by strain gages and by X-ray measurement.