Development of the measurement technique for residual stress in actual components by hole drilling method: (Measurement procedure for improvement of accuracy)

Nuclear power plants that have been shut down due to the East Japan Earthquake have begun to gradually restart. There is concern about accidents due to stress corrosion cracking when nuclear power plants are restarted. Stress corrosion cracking is prevented by shot peening that gives compressive residual stress. However, it is concerned that the residual stress induced by the peening may decrease during long term operation. In order to ensure the safety of nuclear power plants, it is important to evaluate the residual stress on the structure surface. It is possible to evaluate the change of the peening effect by measuring the residual stress on the decommissioning material. There are several methods for measuring residual stress. The hole drilling method is a method of measuring a residual stress from a strain change caused by drilling a surface of a measurement object. In the hole drilling method, a measurement error may occur depending on the state of the measurement object and the measurement method. In this study, a method for improving the residual stress measurement accuracy by the hole drilling method was examined based on the principle of the measurement. As a result, the accuracy of residual stress measurement was improved by measuring the drilling hole diameter and drilling depth with high accuracy, and by correcting the eccentricity of the drill.