| Integrated eddy current non-destructive testing (IECNDT) including allthe advantages of different NDT techniques has been going to be theinevitable trend of eddy current non-destructive techniques in future.Integrated eddy current non-destructive testing technique has not only thecapability of single eddy current testing technique, but also higheraccuracy through the unifying data interface and data fusion. Accordingto the inspecting practical needs of miniaturization, in-situ and fastoperation, some in-depth studys on several crucial issues of IECNDT systemhad been made, for instance, system model analysis, eddy current testingsystem optimization and several other key aspects. The main researchcontents and innovations are as follows.Based on analysis of the physical and theoretical basis of the ECT,the common physical models and calculation methods of ECT are discussed.The impedance characteristic of the sensor and induced eddy currentdistribution researched. Some optimizations for ECT system are carried outincluding digital controlled bridge and the pulsed signal generator. Basedon Maxwell law, the electromagnetic potential function is used to expressthe time harmonic electromagnetic problem excited by sine signal and thetraditional coil sensor is expressed by a simplified axisymmetric model.The impendance and magnetic field distribution affected by eddy currenteffect are analyzed. In the paper, optimizations for ECT system are carriedout including a digital controlled bridge and the pulsed signal generator,which are based on the analysis of ECT system structures. All the researchwould support the work of integrated eddy current testing technique.A novel common principle-layer model and a common function-layer modelare proposed. Based on the models, a deep study on dual-bus and dividedlayer system architecture was carried out. A novel integrated eddy currentsignal generator signal generator and conditioner. There are differencesbetween different ECT techniques. Through analyzing principle of ECT, basedon the design thinking of integration, fast inspection and replaceconfiguration, a novel common principle-layered model is proposed. Throughanalyzing function of ECT system, a novel common functional layered model is brought forward. And then, dual-bus and divided-layered systemarchitecture studied. A design of integration eddy current signal generatorand conditioner is made based on the models, which support the work ofintegrated eddy current testing technique.IECNDT systems based on the thought of fast operation, modulation aredesigned and implemented. It is a hotspot to employ multiplenon-destructive testing methods for enhancing the probability of detection;meanwhile, there are increasing requirements of rapidity, intelligence andintegration in in-situ aviation NDT. A novel integrated ECNDT system wasdeveloped based on the universal model of eddy current testing system inprinciple and function. The system has modularized and reconfigurablesystem architectures and employs dual-bus structure: PCI and IIC. Itcontains not only functions of PECT, general ECT, MFECT, ACFM and AECT,but also integration of multiple ECNDT methods, like PACFM (PEC and ACFM).The system of integrated eddy current nondestructive testing has beensuccessfully used in some aviation filed, which has obtained a goodevaluation.Traditional alternating current field measurement (ACFM) technique hasadvantages of quantitative defect detection and non-contact feature, butpoor detective performances on deep-layer defects. Pulsed eddy currenttesting (PECT) has a better detectability in deep-layer defect, but poorerquantitative performances than ACFM, and moreover, it is easily interferedby lift-off due to ultilising transient signal analysis method so asdifficult to be applied practically. A method of alternating current filedmeasurement with pulsed signal excitation was proposed, which implementsdefect detection and quantitative evaluation by means of transient signalanalysis combined with3D magnetic field measurement based on pulsedresponse signal. Some features which can reflect the magnetic fieldtendency were extracted. Through the study we found that Pulsed AC fieldmeasurement has not only an equivalent detective performance on surfacedefects, but also an excellent performance on defect identification andevaluation of deep-layer defect.A deep study of defect detection for deep-layered structure is madeusing proposed PACFM. Some novel characteristic variables, for example, DPV, are proposed. Quantitative evaluation for deep-layercorrosion in aircraft multi-layer structure is extremely important forhealthy monitoring and lifetime prediction of aircraft. A novel AC fieldmeasurement method with pulsed excitation was proposed, which implementsdeep-layer corrosion detection and quantitative evaluation based on pulsedresponse signal using magnetic field measurement method. The feature whichcan reflect the magnetic field perturbation caused by corrosion wasextracted and the research on quantitative length evaluation for deep-layercorrosion on the basis of response signal fromBz probe was made. Moreoverthe experiments for studying the influences of different depth and widthof corrosions on the quantitative length evaluation were carried out.The results of this paper have been identified by experts. The systemprototype has been put into the day-to-day maintenance and periodic testingof a new type of aeroplane in our army, which turely meet the needs of thenon-destructive testing equipment integration, miniaturization, fast andin-situ detection and got the praise from application units. It haseffectively reduced the workload of the maintenance staff and dependenceon operator experience, moreover has greatly shorten the time on-sitemaintenance, improve the detection efficiency. |
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