Estimation of Uncertainty for Contour Method Residual Stress Measurements

This paper describes a methodology for the estimation of measurement uncertainty for the contour method, where the contour method is an experimental technique for measuring a two-dimensional map of residual stress over a plane. Random error sources including the error arising from noise in displacement measurements and the smoothing of the displacement surfaces are accounted for in the uncertainty analysis. The output is a two-dimensional, spatially varying uncertainty estimate such that every point on the cross-section where residual stress is determined has a corresponding uncertainty value. Both numerical and physical experiments are reported, which are used to support the usefulness of the proposed uncertainty estimator. The uncertainty estimator shows the contour method to have larger uncertainty near the perimeter of the measurement plane. For the experiments, which were performed on a quenched aluminum bar with a cross section of 51 x 76 mm, the estimated uncertainty was approximately 5 MPa (sigma/E = 7 center dot 10(-5)) over the majority of the cross-section, with localized areas of higher uncertainty, up to 10 MPa (sigma/E = 14 center dot 10(-5)).