A hybrid surface fitting approach in the contour method for residual stress assessments

The contour method has been a widely applied residual stress measurement technique over the past 25 years. Recent advancements have focused on improving repeatability and quantifying uncertainty. Traditional analytical techniques may be affected or undermined by contour cutting interruptions. To address this, a hybrid surface fitting routine has been developed, combining two different surface fitting models to represent both high stress gradient at specific regions of interest and smoothing irregularities at less critical areas. A demonstration on a 30 mm-thick SA508 Gr.3 Cl.1 weldment, cut with self-constraint features, shows that the hybrid method provides higher resolution in resolved stresses compared to singular fitting approaches, which can be compromised by cutting-induced plasticity. The hybrid fitting method proves effective in processing data with local irregularities, such as unintentional cutting interruptions, by locally applying a lower-weighted surface function at the most affected regions while maintaining finer details with a secondary fitting function elsewhere. This advancement represents a further improvement and may improve the interpretation of contour method results.