Research Of Eddy Current Non-destructive Testing Methods On Metal-metal Bonded Multilayers

Non-destructive testing and evaluation(NDT&E)is a kind of technology that gets information of surface defects or inside defects of one test specimen through physical or chemical non-destructive methods.NDT&E technology can predict the service life and other parameters of the specimen with the analysis of defect information.Due to that defect information of components under complex work condition can be detected with NDT methods,NDT technology plays an important role in defence industry,nuclear industry and other fields.Eddy current testing(ECT),which is widely used to detect conductive materials,is a common method of NDT.ECT has the advantages of non-contact,low power consumption,no coupling agent and no radiation pollution.Lead-steel bonded multilayer is widely used in nuclear industry because that it can absorb radiation and has high strength.With the influence of manufacturing and transport conditions,there exist cracks and scratchs inside the multilayer.Hence it is urgent to find NDT methods to detect the multilayer.However,the multilayered plate which is bonded by ferromagnetic metal and nonferromagnetic metal has the thickness of 10.3mm.It is challenging for common NDT methods to detect the plate because of its complex geometry.Cracks and scratchs of the plate appear at the inner surface of the steel layer.To find a way to detect inner defects of the multilayer,these following contributions have been done:(1)With the help of Maxwell's equations,basic principles of remote-field eddy current(RFEC),split transmit/receive(T/R)eddy current testing and ring ECT have been formulated.With the analysis of multilayer,RF-T/REC method and ring ECT method are pressed.Structure and geometrical parameters of these two models are optimized with the finite element analysis(FEA)software COMSOL Multiphysics 5.0.The sensibilities of given defects of two models are calculated.With the comparison of sensibilities of the two models,ring model is choosed instead of RF-T/R method.(2)According to the simulation results,the testing system,which includes one signal source,one power amplifier(PA),one EC probe,one signal conditioning circuit,one data acquisition(DAQ)card,one XY platform and one upper computer,is built.To build this system,the EC probe is manufactured,a PC program is written to collect data,a MATLAB script is written to help C scanning.(3)Through the experiment with the ring ECT system,multilayered plates are detected with C scanning and multilayered curved specimen is inspected with B scanning.The built system can detect all of given defects after the analysis of impedence maps.