Quantitative Analysis And Reliability Evaluation Of Eddy Current Testing For Roulette Closed Cracks

As the aero-engine wheel disc is the core component of the engine,it is very important to establish a wheel detection reliability system to ensure the safety of the engine.In this paper,a simulation model of grooved electrical connection is established,the influence of model parameters on the eddy current detection signal is discussed,the closed crack defects were prepared,the eddy current detection of the closed crack is carried out and its eddy current characteristics are analyzed,and the reliability of the eddy current detection of the disc defect is carried out.The simulation and experimental research of eddy current testing system were carried out and the data transfer function of artificial groove and closed crack was established,and realized the evaluation of the reliability of the existing eddy current testing system.Firstly,according to the defect characteristics of closed cracks,a simulation model of grooved electrical connection is established.According to the different crack closure states,a uniform electrical connection model,a laminated electrical connection model and a point area electrical connection model are set up respectively.The influence of each parameter on the eddy current testing effect of different models is analyzed,and the results show that when the degree of electrical connection of defects increases,the amplitude of the eddy current testing signal in the uniform electrical connection model shows a downward trend;when the electrical connection coefficient of each layer increases,the inner area area When the proportion decreases and the number of closed layers increases,the amplitude of the eddy current signal decreases in the stacked electrical connection model;when the radius of the point area increases,the point area moves upward,and the electrical connection coefficient of the point area increases,the electrical connection in the point area increases.The amplitude of the eddy current signal in the model is reduced,which further ensures the rationality of the electrical connection simulation model through research.Secondly,the fatigue scheme is set according to the closed crack principle,the closed crack test block is reasonably prepared,and the relationship between the crack length and the eddy current signal amplitude is obtained;Combined with simulation analysis,the three-layer laminated electrical connection groove model is selected and the optimal model parameters are determined,which can better represent the linear relationship between the actual closed crack length and eddy current testing;The closed crack eddy current characteristic test was carried out,and the law that the magnitude of the tensile load was positively correlated with the rate of change of the eddy current signal amplitude was obtained through the tensile test.The oxidation test was carried out to analyze that the oxide film effectively weakened the electrical connection state of the closed crack,resulting in a larger amplitude of the eddy current signal.It was verified by EDS that there were differences in the degree of oxidation reaction in different regions,and it was confirmed that the oxide film was the real cause of the increase in the amplitude of the eddy current detection signal.Finally,a reliability simulation research system for eddy current testing of wheel discs is established,the influence of uncertain factors in the testing process is reasonably considered,and the differences in eddy current testing laws for different types of defects are compared.The influence of defect width and electrical connection coefficient on detection reliability is analyzed.When the defect becomes narrower and the degree of defect electrical connection increases,the reliability of eddy current detection decreases,and the minimum detectable size becomes larger.A reliability test research system was built by using a three-dimensional scanning device,and the influence of scanning speed,scanning step distance and lift-off height on the reliability of eddy current was studied.After eliminating the interference factors of personnel and instruments,it is concluded that higher-speed scanning,larger scanning step distance and higher lift-off state will all lead to a decrease in the reliability of eddy current testing;Defects in three different states were prepared,and the probability of detection(POD)curve of the closed crack detection of the central hole of the aero-engine wheel disc was obtained by the transfer function method.