Research On Composite Eddy Current Testing Method For Ferromagnetic Plate Defects

Steel plates are widely used in various fields of the national economy,and are indispensable industrial raw materials in machinery,chemical industry,bridges,construction,ship and vehicle manufacturing,and aerospace.However,due to the residual stress in the production process and the fatigue and corrosion in the use process,various types of defects will be caused on the surface of the steel plate.When a steel plate with defects is subjected to load or pressure,there is a possibility that the defect will deform or break,which will affect the production efficiency at light,and cause safety accidents at worse,and even cause heavy losses.Therefore,it is necessary to carry out quality inspection of the steel plate.At present,the most suitable method for steel plate quality inspection is eddy current inspection,which has high detection sensitivity,non-contact,and is easy to realize automated non-destructive inspection.On the basis of fully investigating the research status of composite eddy current nondestructive testing at home and abroad,this paper proposes a composite eddy current nondestructive testing method to solve the problem that surface defects and deep defects cannot be detected simultaneously in ferromagnetic flat eddy current testing,which is verified by simulation and experiment.The effectiveness of the proposed method is studied as follows:Firstly,the recent research progress in the field of flat eddy current testing at home and abroad is studied.Combined with the high precision of conventional eddy current for surface defect detection and the great detectable depth of far-field eddy current,a composite eddy current testing principle is proposed.The feasibility is demonstrated based on the perspective of energy flow,which provides a theoretical basis for subsequent system development.Then,the composite eddy current testing simulation model is established,the testing frequency and probe design parameters required to realize the composite testing are determined through the simulation,and the design method of the optimal magnetic core structure is proposed.Through comparative experiments,it is determined that the optimal combination of magnetic shielding materials for shielding effect is the combination of inner copper and outer silicon steel,and finally the design of the composite eddy current detection probe is completed.Then,a classification method of surface and deep defects in composite eddy current inspection of flat plate defects is proposed.In the finite element simulation software,the influence of the width change and the depth change on the detection signal in the composite eddy current testing is simulated respectively.The research shows that in the composite eddy current testing model,the width of 1 mm～5 mm and the depth of 1 mm～8 Conventional eddy current surface defect detection and far-field eddy current surface and deep defect detection for defects in the range of mm can realize the classification of surface and deep defects through detection signals,and the reliability of the classification method is verified by pseudo-random defect simulation.Finally,an eddy current composite detection system for flat plate defects is built,and composite eddy current testing experiments are carried out on steel plates with different defects.The relationship between the signal and the size of the defect at different locations.The experimental results are consistent with the simulation,which proves that the composite eddy current testing method can quantitatively detect the defect width and depth of the surface and deep defects of the flat plate,and can distinguish the detected surface defects and deep defects.