Release coefficients during measuring non-uniform residual stress with blind-hole method

Integral method is widely used in calculating the non-uniform residual stresses from the measured relaxed strains using the blind-hole method,in which the release coefficients have great influence on the measurement accuracy. As the residual stresses in each layer are assumed to be uniform when calibrating the coefficients,the calculated results are considerably different from the real stresses if the residual stresses vary rapidly along the depth. In this paper,a three-dimensional FEM model was established for the release coefficients,and verified by a simulated test on a uniform loaded plate. The errors in the calculation of the non-uniform residual stress field were studied using the release coefficients calibrated by the integral method, and then an improved technique was proposed to recalibrate the release coefficients. The results show that the calculated residual stresses using the recalibrated coefficients are closer to the real ones.