Research On The Key Technology Of Remote Field Eddy Current Testing Of Aircraft Multi-Layer Riveted Structure

The safe flight of aircraft is the lifeline of aviation equipment,and regular inspection and maintenance of key aircraft components is the basic guarantee for the sustainable development of aviation.As an important structural part of the aircraft under the action of complex load and service environment,the multi-layer riveting structure of aircraft is seriously concentrated,and fatigue cracks are easy to germinate,resulting in the reduction and even loss of the strength and stiffness of its key components,thereby affecting the integrity of the aircraft structure and endangering flight safety.Therefore,it is urgent to carry out in situ detection technology for aircraft multilayer riveting structure to achieve the characterization and quantitative evaluation of its internal damage defects.Traditional non-destructive testing methods such as conventional eddy current testing,ultrasonic testing,penetration testing,radiation testing,etc.are limited by the inspection technology itself,and it is impossible to complete the detection of deep defects in the multi-layer riveting structure of the aircraft without disassembling.The remote field eddy current(RFEC)detection technology based on the indirect coupling energy secondary penetration mechanism breaks through the limitation of the effect on conventional eddy current testing,and combines the advantages of low cost,high detection efficiency and fast detection speed of conventional eddy current testing,making it particularly suitable for in-line detection of deep hidden defects in aircraft multilayer riveting structure.In this paper,taking the multilayer riveting structure of aircraft as the research object,based on the generation mechanism of the remote field eddy current phenomenon of pipeline class,the realization of the remote field eddy current phenomenon on the multilayer riveting structure of aircraft is studied.Based on electromagnetic shielding theory,a new remote field eddy current sensor model for aircraft multilayer riveting structure detection is proposed.Through the simulation software,the effect of the excitation coil,detection coil,core and shielding structure size on the remote field eddy current phenomenon in the remote field eddy current sensor model is studied,and the parameters of each size are optimized from the energy propagation angle,and the overall size of the remote field eddy current probe is68mm×34mm×26mm after optimization.Based on the optimized remote field eddy current sensor,a three-dimensional finite element model of hidden crack defect detection of aircraft multilayer riveting structure is established,the defect detection process is simulated by simulation software,the signal characteristics of remote field eddy current sensor defect detection are obtained,and the response law of different sizes and buried deep crack defects is simulated and analyzed from the detection signal amplitude and phase angle.In order to verify the correctness of the simulation model,the experimental study of remote field eddy current detection of aircraft multilayer riveted structure was carried out,defect specimens containing different types of crack defects were designed and produced,and the remote field eddy current sensor was processed and assembled.According to the experimental requirements,a remote field eddy current detection hardware platform including sensor components,signal conditioning circuits,lock-in amplifiers,host computers,and a three-axis electronic control motion platform was built,and the Lab VIEW programming software was used to design and develop the remote field eddy current detection platform software.Finally,the built remote field eddy current inspection system is used to detect crack defects of different lengths,widths,depths and burial depths on the defect specimen.The experimental results show that the designed remote field eddy current probe can detect crack defects with dimensions of10mm×1mm×0.5mm(length × width × depth)under three layers of 10 mm thick 2024 aluminum alloy flat plates,and with the increase of defect size and burial depth,the peak of the detection signal amplitude and phase also increases,which verifies the accuracy of simulation results and the feasibility of the remote field eddy current probe model.