| Most aircraft skins are assembled from riveted structural parts,and riveted holes are prone to cracks due to stress concentration.Therefore,it is urgent to carry out nondestructive testing of aircraft riveted parts.In this paper,a focusing remote field eddy current detection probe is designed to study the hidden defects around the holes of aircraft riveted components,and a three-dimensional model of focusing remote field eddy current detection for hidden defects of aircraft riveted parts is established.Based on the structural parameters,a focused far-field eddy current testing system was designed and built,and an experimental study of focused far-field eddy current testing was carried out.The inversion of defect length and buried depth was achieved by analyzing the detection signals of the array detection coils.The simulation model of ANSYS focused remote field eddy current testing was established,the magnetic field superposition characteristics of the focused remote field eddy current probe were studied,the influence of the magnetic circuit structure of the excitation unit on the energy and distribution of the focused magnetic field was analyzed,and the focused remote field eddy current was optimized.The structural parameters of the probe,such as the height of the excitation coil,the angle of inclination and the spacing,are used to detect the defects by the excitation-rivet-detection rotation detection method.According to the simulation results,by comparing the magnetic field strength under different thicknesses of aluminum plates,the parameters such as the height of the excitation coil and the pitch angle of the focused remote field eddy current probe were optimized.The experimental research and comparison with the detection ability of the non-focusing probe show that the detection ability of the focusing far-field eddy current probe is better than that of the non-focusing probe.At the same time,a focusing remote field eddy current detection system suitable for the focusing probe is designed,which includes: excitation module,signal conditioning module,acquisition module and detection software,realize the functions of focusing far-field eddy current probe excitation,detection signal processing and defect visualization.The riveted specimens were designed and processed according to aviation standards,and the test specimens were studied by using the developed focusing farfield eddy current testing system and focusing remote field eddy current probe.The excitation frequency of the focusing remote field eddy current probe was optimized,and the defect detection capabilities of the single-channel focusing and non-focusing far-field eddy current probes at different burial depths were compared.A multi-channel array focusing eddy current detection probe was designed,and different defect lengths and burial depths were studied.The influence law on the detection signal of each channel of the array probe is presented,and the defect inversion method is also proposed.The test results show that the optimal detection frequency of the focusing remote field eddy current probe is 400 Hz,which can effectively detect defects of5×0.2×1 under the burial depth of 9mm.For non-focusing remote field eddy current probes;the defect length can be obtained by analyzing the signal attenuation law between channels,and after the defect length is known,the depth of the defect is evaluated by the detection amplitude of the peak channel,which is a rotating array focusing remote field eddy current defect.Inversion provides some reference. |
