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.

Residual Stress in Engineering Materials: A Review

“…It was also clarified that these errors are a function of the ring geometry, material properties, and maximum residual stress magnitude. [ 95 ] Bouffioux and teammates measured residual stresses on long‐rolled profiles conducting X‐ray diffraction (XRD), ring core (with strain gauges), and sectioning methods. They reported that the ring core measurement results agree with numerical models, both in longitudinal and in transverse directions, suggesting that this method is well adapted to this kind of piece.…”

“…The residual stress response due to WEDM cutting is discussed in the study by Salvatti et al [232] Over recent decades, various destructive and nondestructive methods aimed at measuring the machining-induced surface, and internal residual stresses have been developed. Moharrami et al [95] utilized the ring core method to measure residual stress in the milling of narrow circular grooves in which the error value was lower than 1.5%. Chupakhin et al used the hole drilling method to study the effect of material behavior on the residual stress profile determination.…”