Research On Pulsed Eddy Current Testing Of Aircraft Multilayer Metal Structure

It is difficult to detect flaws buried in the multi-riveted structure of aircraft. Pulsededdy current technology is a new type of electromagnetic nondestructive testing, whichuses a certain duty cycle square wave pulse as the excitation and has the advantages ofwide spectrum and effectively deep detections. And it can certainly detect the burieddefects in multilayer metal structures.In this paper, the history and research status home and abroad as well as the currenthot research topics of pulsed eddy current are firstly described. Based on the pulsededdy current principle, a complete detecting system is established in order to detectinner cracks and corrosions in the multi-layer aluminum structure, which includeshardware instruments and software platform. The hardware instruments consist of pulsesource，signal conditioning circuits, hall sensors and multi-riveted aluminum structure;The software analysis platform consists of data acquisition program, detection systeminterface and data processing. The probes are designed to both cylindrical andrectangular types whose structure parameters are optimized by analyzing the excitationcoil diameter, the number of ampere turns, as well as the signal to noise ratio. After theacquired signal was filtered de-noising based on wavelet analysis method and usefulinformation is retained, an approach using peak compensation based on the lift-offreference signal was proposed in the lift-off test, and the effect of suppression ofprobe’s is comparatively analyzed. Experimental results show that the algorithm is ableto suppress the probe’s lift-off and it can be effectively used in the lift-off detection ofinner flaws in the multi-layer metal structure. The peak and peak time of defects fordifferent burial depth are obtained in the many times of repeated experiment, and innerdefects are identified. The consistency of experimental results and theoretical analysisverity the correctness of the methodology used in this paper. In addition, the signal fromlinear array sensor is divided into different time slices in time periods, to obtain thecharacteristics of the defects depths, and then compose an amplitude matrix as to realizethe imaging scan of defects in different burial depth in real time.Finally, the conclusion of this paper is given and suggestions for the further workof research is provided.