Research On Conventional/Remote Field Dual-mode Eddy Current Testing Method And Reliability Analysis Techniques

Eddy current non-destructive testing (ECT) is widely used in the fields of aviation, nuclear industry, petrochemical engineering and machine manufacture. Based on defect recognition and quantitative estimation, a theoretical and experimental study on defect detection in plate-like conductors is performed by using the eddy current technique. The project is supported by the National Natural Science Funds. Conventional/Remote field dual-mode eddy current system has been built and experimentally verified, the system has been optimized by the taguchi method. The probability of detection (POD) has been used to evaluate the reliability of the ability of defect detection.The main work and results of this thesis are as follows:(1) The basis theory of conventional and remote-field eddy current testing have been researched.The feasibility of dual-mode EC detection system has been analized and verified. The principle and analysis provide a therotical basis for the development of dual-mode EC detection system.(2) In order to combine the advantages of conventional ECT and remote field ECT method to enhance the capabilities of defect detection with different types and depth, a convention/remote field eddy current prototype testing system has been developed. The excitation signal generation, detection signal processing technology, acquisition and display of the detection signal and the design of compound probe have been researched.(3) For improving the overall performance of dual-mode system, the Orthogonal design method has been studied which has been used to optimize the voltage amplitude and frequency of excitation signal etal. The optimization result showed that the method can improve the capability of defect detection which has been verified by the statistical experiment.(4) POD theory has been introduced to evaluate the reliability of conventional ECT/remote field ECT instrument. The process for building the model of POD curve has been described in detail, especially the POD modeling based on experiment data and function model method, which has been used to evaluate the reliability of the detection capability.The defect detection experiments and analysis have been studied based on plate-like conductors, the results showed that conventional/remote field dual-mode eddy current testing method can simultaneous detect the upper surface defects and lower surface defects, and the ability to detect the lower surface defects has been improved.