16. Repeatability of Contour Method Residual Stress Measurements for a Range of Material, Process, and Geometry

This paper examines precision of the contour method using five residual stress measurement repeatability studies. The test specimens evaluated include: an aluminum T-section, a stainless steel plate with a dissimilar metal slot-filled weld, a stainless steel forging, a titanium plate with an electron beam slot-filled weld, and a nickel disk forging. These specimens were selected to encompass a range of typical materials and residual stress distributions. Each repeatability study included contour method measurements on five to ten similar specimens. Following completion of the residual stress measurements an analysis was performed to determine the repeatability standard deviation of each population. In general, the results of the various repeatability studies are similar. The repeatability standard deviation tends to be relatively small throughout the part interior and there are localized regions of higher repeatability along the part perimeter. The repeatability standard deviations over most of the cross-section range from 5 MPa, for the aluminum T-section, to 35 MPa, for the stainless steel forging. These results provide expected precision data for the contour method over a broad range of specimen geometries, materials, and stress profiles.