Method For Obtaining Residual Stress In Welded Joints By Combining Indentation Test And Surface Strain Measurement

Nuclear welding material will generate relative compressive or tensile residual stress inside the material after forging,bending,and welding,thus affecting the normal operation of the safety end equipment.Therefore,it is of great significance to seek a convenient,fast,and reliable residual stress test method for the life evaluation of equipment.The indentation strain method has the advantages of convenient operation,simple operation,and high measurement accuracy,and is suitable for the measurement of residual stress in in-service nuclear power equipment.In this study,based on the principle of indentation strain,numerical simulation and physical test were used to explore the variation law of the strain during the indentation process,and the effect of the indentation depth on the strain under the residual stress state,residual stress calculation model is established,and the model is applied to the detection of the residual stress of the welded joints at the safety end of the nuclear power structure.The main research contents are as follows:A three-dimensional model of the press-in test with residual stress was established by using the finite element software to simulate the indentation test with a ball indenter at different indentation depths.The change of strain in the direction of the principal stress of the specimen after the unloading of the indenter was obtained,and the change law was studied to find the best location of the strain measurement point.The change law of strain during the indentation process was analyzed by using the three-dimensional model.The relationships between residual stress and the slope of displacement-strain curve K’ were explored by combining the effect of residual stress on the displacement-strain curve,and the calculation model of residual stress was established.316L austenitic stainless steel material was taken as an example,and the indentation test with residual stress was completed using the indentation test platform modified by the electronic universal testing machine and the residual stress loading device developed and designed by the laboratory itself.The strain gauges were attached to the specimen at the standard distance section,and a static strain tester was used to collect the changes of strain at the strain gauges during the indentation process.The test results were analyzed and compared with the simulation results.The dissimilar metal welded joints of nuclear power safety end was taken as an example,and a simplified sandwich model of the safety end welded joint was established.The residual stress of welded joints was distributed into the sandwich model,and the indentation test was conducted on the model to obtain the displacement-strain curves in each area of the model,and then the accuracy of the empirical formula for predicting the residual stress of welded joints was verified.