Research Of Nondestructive Testing For Aircraft Skin Based On Array Eddy Current

As one of the five classical non-destructive testing technologies, eddy current testing has the advantages of needless of couplant,high speed, low cost and apt for automatic testing, etc. The array eddy current sensor is suitable for scanning large area of conductive material.The conventional array eddy current sensor is just the simple sum of several individual coils. More defect information can be gathered by measuring the mutual inductance between array coils. Combination of several coils as diver-receiver pair makes it possible to test the cracks in various directions which maybe blindness for the conventional sensor. Based on The Maxwell equations and eddy current effect, the principle of the array eddy current testing, especially the mutual inductance theory, are described. Defects and sensors models tending to test the aircraft skin are simulated using FEM and ANSYS software.Due to its complexity and flexibility, only partial of the array eddy current sensor consisting of 3×3 coils is studied. The sensitivity of the sensor is a function of the coil's geometry, distance between array coils, lift-off effect as well as the frequency of excitation. After analyzing these factors respectively, the corresponding change of the induced potential amplitude is achieved, and the eddy current distribution is displayed visually. As a result, the parameters of array coil are designed, and the height of lift-off and the excitation frequency are set.Aiming to disclose the defects of aircraft skin such as fatigue cracks, corrosion, debonding of the bonding layer, the artificial defects are designed and simulated with three-dimensional FEM. The induced potential amplitude variation of each coil and the eddy current distortion are acquired corresponding to the different defects. The use of the mutual induced potential provides more information for the image reconstruction software, and more precise images can be achieved.