Residual Stress Measurement in Tubular Members

When prismatic members are sliced longitudinally for the purpose of measuring residual stresses, a curvature often develops in the strip. This curvature is caused by a gradient of residual stresses through the wall thickness, so that surface strain measurements alone can grossly misrepresent the true average strain. An additional measurement of the offset of the sliced strip from its initially straight position provides a second independent distortion quantity and enables a separation of average and gradient components of residual strain. The test includes the equations required for data reduction, an analysis of the error involved in neglecting varying amounts of curvatures and the precision required in measurements. The technique was applied to rectangular structural tubing with satisfactory results.