Research Of Calibration Coefficients For Measurement Of Non-uniform Residual Stress By Blind-hole Method

Blind-hole method is featured by simplicity of operation and lower damage tocomponents and is widely used in measuring residual stresses. There are manyfactors which affect measurement accuracy of blind-hole method. Among them,calibration coefficient is one of the main factors. For the calibration of releasecoefficient, the standard CB3395-92is adopted in China, while the ASTM standardE837-81is mainly accepted in the foreign countries. Calibration of release coefficientis based on the assumption that residual stress is characterized by uniform distribution.But the distribution of residual stresses in the actual structure is non-uniform alongwith the depth. In this case, errors will be produced by employing the releasecoefficient which is got from adopting calibration methods in the standards tocalculate the residual stresses. To solve this problem, the finite element numericalsimulation method is used to research the release coefficient in the non-uniformresidual stresses in this thesis. To verify the effectiveness of numerical simulationmethod, the simulated calibration of release coefficient in uniform stress field wasconducted firstly and the calibration result were compared with the existingexperimental calibration value and recommended value in the standard ASTM. Basedon the integral method, the errors caused by release coefficient of residual stressesfield which linearly varies along with depth were studied, and the method to modifythe release coefficient in non-uniform stress field was proposed and testet.The results show that the release coefficient produced by using finite elementnumerical simulation method in uniform stress field has a great agreement with theexperimental calibration result; thus method of using the finite element numericalsimulation to calibrate release coefficient is completely feasible. But, if the releasecoefficient calibrated in uniform stress field is still used in the calculation of residualstresses in non-uniform stress field, significant errors will be produced. Residualstresses which are calculated by employing the release coefficient calibrated by usingthe modified method proposed in the thesis is much closer to the real values.