Pulsed Eddy Current Testing Research Based On Analysis Of Feature Parameters And Dynamic Characteristics

Because of the different types of interference signals, it is difficult to analyze the recognition and quantitative of different types of defects in multi-layer metal riveting structure plane which is in the aerospace nondestructive testing(NDT) field.Therefore, the study on the effective methods to suppress different types of interference is extremely urgent. Pulsed eddy current(PEC) testing has a lot of technical advantages, such as wide spectrum, convenient, fast detection and so on. It has become a hot topic in nondestructive testing field.In this paper, the analysis and inhibition of interference signal has been put forward after consulting a large number of domestic and foreign documents.The lift-off effect analysis, which based on system identification, has been adopted in this paper. By using the signal tested by sensors in the air as input signal and the signal tested at different lift-off heights as output signal, the least-squares method were used to estimate the parameter of the model, ARX model with different parameters is obtained. The result of the model shows the frequency characteristics of systematic models can be used to indicate different lift-up height of defects in deeper position inside the specimens during the test.The method of extracting the slope of the differential signal peak value is used to analyze the lift-off effect. A database is established by the rule that the corresponding differential peak slope of different defects decreases with the increasing size of the defect. The experimental results show that lift-off effect suppression is well in surface crack.Lift-off effect is analyzed the by the method of signal peak normalization. Take the signal from the air and the surface of specimens which has not defect as input signal to inhibit the lift-off effect. The results show that, the suppression effect of internal corrosion works well, which can be used for suppression of the "lift-off" effect of internal defects.The method of dynamic trajectory characteristic vector is used to suppress the edge effect in PEC. Transforming the scanning path of probe with the method of FFT,analyze the feature vector which consist of amplitude and phase composition in everyharmonic. Identify the difference between interference signal and flaw signals by analyzing the trajectory. According to these differences, we can suppress the edge effect by three steps. Firstly, translate the defect trajectory of edge effect. Secondly,make a synthesis of signals after IFFT transformation. Lastly, check its information with differential signal containing defects. The results show that the signal after the edge interference suppression coincides with differential signal only containing defects. We can see that the Inhibition affects well which proves that this algorithm is effective.Finally, this paper made a summary, and provided some suggestions for further research.