Research On Internal Defect Detection Of Multilayer Dissimilar Metal Materials Based On Pulse Eddy Current

The multi-layer heterogeneous metal bonding structure is widely used in aerospace,military,nuclear industry and other important fields because of its high specific strength,high specific modulus,anti-fatigue and anti-knock performance.It can detect and ensure the safety and reliability of structural quality significant.It is of great significance to detect and ensure the safety and reliability of the structural.Due to the influence of the production process and environmental factors,the bonding of the laminates tends to produce defects such as poor adhesion,pores and local debonding.During the manufacturing,assembly and service process,it is easy to occur cracks,scratches and other injuries because of mechanical processing,collision and fatigue loading.These defects are hidden in the surface of the laminates,adhesives and inside the plate,will lead to changes in the structure of the thermal and mechanical properties,This will affect the integrity of the structure,reliability and security.So as the foundation of science and technology of nondestructive testing technology has been more and more important.Pulse eddy current detection is an important branch of nondestructive testing technology.Compared with other detection methods,it has the advantages of fast detection speed and deep detection depth,etc.In this paper,the detection of pulsed eddy current is studied.Specific work as follows:(1)Based on the theory of pulsed eddy current,a two-dimensional axisymmetric detection model was built using COMSOL software.The influence of the structure parameters of the pulse eddy current sensor on the detection results is discussed through simulation.And get a set of optimal value at last.(2)According to the simulation results,the pulse eddy current detection system is built.Including the acquisition of the excitation signal,the excitation signal power amplification,the data acquisition,the host computer software,and use the standard sample to verify the correctness of the system.(3)Using the pulsed eddy current detection platform constructed in this paper,five defects were tested.And analyze the data from the time domain and frequency domain.In the time domain,the feature quantity used in this paper is the peak amplitude of the differential signal.In the frequency domain,the feature quantity used in this paper is the amplitude of the fundamental component,the third harmonic amplitude and the ratio between them.Through the experiment,the pulse eddy current detection system designed in this paper can detect the depth of non-ferromagnetic material up to 8mm(experimental standard specimen: aluminum alloy),And for different depth defects,the response signal amplitude in the time domain is linear.For the first two-layer debonding defects of multi-layer dissimilar metal materials,the system covered by this article can successfully detect defects with diameters of 5 mm,4 mm and 3 mm,diameter of 2mm,1mm defects can not be detected.