A procedure for high residual stresses measurement using the ring‐core method

Abstract The ring‐core method is a mechanical technique used to determine the residual stresses on the surface of materials by milling a narrow circular groove around the point of interest and monitoring the strain variation. Original stress can be evaluated by using the relaxed strain through the linear elasticity theory. In case of a highly stressed field, the yielding of the material around the groove and its bottom causes an error related to the hypothesis of the basic theory of the method. In this paper, the plasticity effect of calculated residual stresses was considered. For this purpose, the ring‐core development and stress relaxation in a generally stressed body were simulated using a 3D parametric finite element model and the stress calculation errors were obtained by comparing calculation stress with the actual one. According to the results, the error value was affected by some parameters such as ring depth, stress magnitude and state, and material behaviour. In general, for residual stresses above 65% of the local yield strength, the plasticity‐induced errors were significant, as an error close to 35% was found. Based on the result, a correction procedure was proposed for the evaluation of the high level residual stresses in steel materials by the ring‐core method. By the method, true stresses can be obtained with considering the calculated stresses state, material properties, ring geometry, and estimated plasticity‐induced errors.