1、Pulsed eddy current technique for defect detection in aircraftriveted structuresYunze Hen,Feilu Luo,Mengchun Pan,Feibing Weng,Xiangchao Hu,Junzhe Gao,Bo LiuCollege of Mechatronics and Automation,National University of Defense Technology;Changsha 410073,Chinaa r t i c l e i n f oArticle history:Recei
2、ved 1 July 2009Received in revised form29 October 2009Accepted 30 October 2009Available online 12 November 2009Keywords:Nondestructive testingPulsed eddy currentDifferential probeDefect detectionRiveted structurea b s t r a c tThe Pulsed Eddy Current(PEC)technique is an effective method of quantifyi
3、ng defects in multi-layerstructures.It is difficult to detect defects in riveted structures of aging aircraft.Based on theoreticalanalysis of PEC technique,three different probes,including a differential hall probe,a differential coilprobe,and a two-stage differential coil probe are designed to dete
4、ct this kind of defects.The averagingmethod and wavelet analysis method are used to de-noise the hall response signals.By selecting peakamplitude and zero-crossing time of response signal in time domain as key features,defects in rivetedstructures can be detected effectively.The experimental results
5、 indicated that the differential coil probeacted as effectively as the differential hall probe.The defects between third layer and fourth layer inriveted structures can be detected by utilizing the two-stage differential coil probe.The PEC techniquehas a promising application foreground in the field
6、 of aeronautical nondestructive testing.Crown Copyright&2009 Published by Elsevier Ltd.All rights reserved.1.IntroductionThe detection of second layer defects and hidden defects inriveted structures has been identified as major problems inaeronautical nondestructive testing.Traditional ultrasonic,ed
7、dycurrent and radiometric methods can detect first layer defects.However,it is difficult for these methods to detect second layerdefects.The pulsed eddy current(PEC)nondestructive testing is anew technology developed in recent years,which is an effectivemethod that has been demonstrated to be capabl
8、e of quantifyingdefects in the multi-layer structures 13.In contrast to theconventional eddy current technique with a single frequencysinusoidal field excitation,PEC technique uses pulsed excitationthat is characterized by the richness of frequency contents 4.Inaddition,PEC technique can minimize po
9、wer consumption,whichis more promising in the development of portable instrument 5.Rose JH et al.described the corrosion characterization inaircraft lap splices for both air-core and ferrite-core PEC probeswith one plat coil 6.Giguere S et al.illustrated three featuresadopted in PEC testing to quant
10、ify defects and exemplify theirapplication 7.Sophian A et al.presented a new type of pulsededdy current sensor for defect detection in aircraft lap-jointstructures 8.Tian GY et al.presented a new feature called asrising point time to identify the different defect types and lift-off,which offers bene
11、fits such as independence of coil dimension andability to evaluate a defects depth regardless of its type or shape9.Zeng ZW et al.presented a three-dimensional finite-elementmodel of Maxwells equation for numerical simulation of theMagneto-optic/eddy current imaging(MOI)operation which wasuseful to
12、detecting surface and subsurface cracks at rivet sites10.Li S et al.introduced development of differential probes inpulsed eddy current testing for noise suppression 11.In all thesestudies,the driving coil is excited by repeated pulses and theresponse signals are measured with different sensors,whic
13、h maybe the driving coil,another coil,or a hall-effect sensor.However,differential coil probe and two-stage differential probe have notbeen proposed to detect the defects in airframe riveted structures.The main purpose of this paper is to detect the defects inairframe riveted structures.First and fo
14、remost,pulsed eddycurrent principle is introduced in Section 2.Next,three kind ofdifferential probes are proposed and designed in Section 3 and thePEC detection system is presented in detail in Section 4.Then,experiment results and discussion are shown in Section 5.Finally,conclusions and further wo
15、rk are outlined in Section 6.2.Pulsed eddy current principleThe PEC probe is excited with a repetitive broadband pulse.Since a broadband frequency spectrum is produced in one pulse,the response signals contain important information of defects12.Typical features such as peak amplitude and zero-crossi
16、ngtime are used to detect and characterize defects 13,14.The keyfeatures(peak amplitude and zero-crossing time)of responseARTICLE IN PRESSContents lists available at ScienceDirectjournal homepage: International0963-8695/$-see front matter Crown Copyright&2009 Published by Elsevier Ltd.All rights reserved.doi:10.1016/j.ndteint.2009.10.010nCorresponding author.Tel.:+86 13467698133.E-mail addresses:(Y.He),(F.Luo).NDT&E International 43(2010)176181ARTICLE IN PRESSsignals in time domain are shown in
