A Hybrid Surface Fitting Approach in the Contour Method for Residual Stress Assessments

Abstract The contour method is gaining wider acceptance as a residual stress measurement technique during its 25 years of development. It offers a complete stress component orthogonal to a cutting plane by reconstructing the stresses based on the out-of-plane displacements using superposition theory. Recent advancements have focused on improving repeatability and quantifying uncertainty. Traditional analytical models often fail to adequately represent measured out-of-plane displacement data with complications. A hybrid surface fitting routine has been developed to address this, combining two different surface models to represent both high stress gradients at regions of interest and smoothing irregularities and noise in lower fidelity regions. This technique has been applied to a 30mm thick SA508 Gr.3 Cl.1 weldment, cut with self-constraint features. It will be shown that this 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. This is because it allows for a local application of a lower-weighted surface function at the most compromised regions, while maintaining finer details elsewhere with a secondary fitting function. This advancement represents an improvement in the reliability and precision of the contour method for residual stress analysis.