To study the effect of stress magnitude and tool geometry on the calibration coefficients: Ring core technique

Ring core technique is widely used to measure the subsurface residual stresses in components. In the analytical evaluation of residual stresses by ring core technique, the calibration coefficients play the vital role for the correct estimation of residuals stresses. Calibration coefficients needed to evaluate the residual stresses by dry ring core technique have been determined with respect to varying ring core tool dimensions. The effect of the biaxial stress combinations and trepan tool diameters on the calibration coefficients was investigated. The trepanning effect of dry ring core process was also investigated through 3D finite element models. The finite element analysis was done to prepare a database of strains for the different stress combinations with respect to the depth of cut. After that the regression equations were developed to directly calculate the calibration coefficients for the material SS 304L. Furthermore, this finite element data was also used to develop the mathematical relations to calculate the residual stresses from the strain readings obtained in dry ring core process. Error estimation of residual stress calculation was also done for both analytical and regression models. The database of relations between residual stress and strains developed in the present study with respect to a given dimension of ring core tool was found to be adequate in estimating the residual stresses directly from the strain reading during dry ring coring.