Pulsed Eddy Current Testing Of Rieveted Multilayer Metal Struture In Aircraft

Riveted multilayer metal structure is major component in airframe, and detectionof hidden defects in the structure has been a challenge for non-destructive testing(NDT). It is urgent to find effective NDT methods to solve the problem. Pulsed EddyCurrent testing is a new method of eddy current testing. Compared with conventionaleddy current testing, PEC has a wide spectrum, faster detection speed, high accuracy ofdetection, and etc.A pulsed eddy current testing system has been developed to detect cracks andcorrosion in multilayer metal structure. Furthermore, detection signal and lift-off effectwere analyzed.Hardware system of the platform mainly consists of computer, pulse signalgenerator, detection probe, data acquisition module and test block module. Based on thecharacteristics of aircraft riveted multilayer structure, three types of probe weredesigned. Software design is based on Labview. Single probe detection system and arrayprobe detection system were designed. The main function of software system is dataacquisition and signal analysis and processing.The crack detection in airframe was studied. The influence of different scanningdirection of TMR magnetic sensor probe on detection of different depth of crack wasanalyzed. Signal change of crack detection was observed and analyzed and the methodto measure length and depth of the crack was determinted.Rotating probe was used to detect crack in rivet hole and length and depth of thecrack was estimated.Using array probe to scan riveted multilayer metal structure to detect corrosion. Byextracting time-slice value of the detection signal to make up data matrix which thenwas converted to grayscale image to achieve a scaning imaging.Suppression of lift-off effect was studied in detail. A new technique for reducingthe lift-off effect based on second-order differential values at starting point wasproposed. lift-off effect suppression on detecting crack and corrosion were studiedrespectively and significant results were achieved.Some suggestions for future work are presented.