Research On Measurement Of Welding Residual Stress Based On Electromagnetic Ultrasonic

There will inevitably be welding residual stress in the welding process of structures.Welding residual stess will severely affect the performance of the structure,which can cause potential safety hazards.Therefore,the measurement of welding residual stress is of great significance.As an emerging measurement method of residual stress,electromagnetic ultrasonic method is nondestructive,efficient and capable of online measurement,which has attracted broad attentions.Aiming at the nondestructive measurement of welding residual stress,research has been launched on welding residual stress measurement using electromagnetic ultrasonic method.The feasibility and accuracy of electromagnetic ultrasonic method are verified by blind hole method and finite element method.The result shows that the distribution of residual stress of welded joints can be effectively measured by the electromagnetic ultrasonic method,which means there is potential engineering application value.The main research works of thesis are listed as follows:(1)The residual stress of Q345R plate butt joint was measured by electromagnetic ultrasonic method.The existing acoustic formula of transverse wave is corrected based on the anisotropy of the welded joint material;Considering the fact that there are obvious differences in the microstructure of different welded joints areas(weld zone,heat-affected zone,and parent zone),the calibration samples are processed separately.The acoustic elastic coefficient and material anisotropy parameters of above areas under 25±2 celsius temperature degree conditions were measured by the tensile calibration experiment.Combining with the transverse wave velocity of welded joint,the residual stress distribution in different areas of the welded joint was obtained.(2)The residual stress of welded joints was measured by blind hole method by which the results of electromagnetic ultrasound method were verified.The strain release coefficient was obtained by calibration experiment,which was corrected by shape-changed specific energy parameter S;Comparing the blind hole method results with the electromagnetic ultrasonic method results,it shows that the residual stress distributions are basically the same.(3)In order to overcome the disadvantages of low comparability between blind hole method result and electromagnetic ultrasonic method result,as well as the limited measuring points of blind hole method,welding simulation software Simufact.Welding was used to establish the finite element model which was based on thermal elastoplastic analysis.Numerical analysis were performed on the residual stress of the welded joint and electromagnetic ultrasonic results were verified.The blind hole method was used to verify the accuracy of the finite element model;The distributions of welding residual stress along the thickness of the welded joint were analyzed,and the average numerical simulation results along the thickness direction were compared with the electromagnetic ultrasonic results.It show that the residual stress distributions of the numerical simulation is coincident well with the electromagnetic ultrasonic method.