The Ring-Core method is a mechanical technique used to calculate the surface residual stresses in a material. In this paper, plasticity effects on the calculated results of the Ring-Core technique were studied by FEM analysis. For this purpose, the coefficients were obtained from an elastic finite element modeling. Then, the execution of the Ring-Core technique using bilinear elasticplastic behavior for the material was simulated and finally the relaxed strains due to ring core milling were obtained. The plastic error due to yielding was calculated by comparing the applied stress and calculated stress from the FE simulation. Also, by using the prepared FE model, the effects of various parameters like state of loading, ring geometry and tangent modulus were investigated. Based on the obtained results, a suitable range for the ring diameter was proposed in order for achieves accurate results.

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.

The ring-core technique is a stress relaxation-based method that is used to determine surface residual stresses in a material based on the linear elastic theory. However, material yielding that is due to ring creation on a highly stressed body would cause some errors. In this article, plasticity effects on high-level uniform residual stresses calculated by the ring-core technique were examined via a numerical analysis. The plasticity error owing to yielding was obtained by comparing the applied stress and the calculated stress derived from finite element (FE) simulation. Moreover, using the prepared FE model, the effects of various parameters, such as state of loading, ring geometry, and tangent modulus, were investigated. The results showed a maximum 30 % positive errors in the calculated residual stresses and the great impact of ring geometry on the plasticity error. Based on the results, the optimized ring diameter and depth for suitable precision were proposed.