Research On Eddy Current Testing Of Carbon Fiber Reinforced Polymers And Aluminum Honeycomb Sandwich Structure

The research objects of the dissertation are carbon fiber reinforced polymer(CFRP)and aluminum honeycomb sandwich structure consisting of CFRP panels and aluminum honeycomb core.Because of the outstanding performance they are widely used in aviation,rail transit,sports and other fields.However,they have defects during manufacturing and are damaged in using inevitably.Therefore,nondestructive testing of CFRP and aluminum honeycomb sandwich structure is very important for guaranteeing the quality and reliability.Considering the electrically conducting property,they can be examined by the eddy current testing(ECT)technique.ECT is advantageous because of its easy operation,single-side detection,low requirement of surface preparation,applicability in harsh environment,and other properties.Hence ECT has a broad prospect of application in the phases of production,using and maintenance of CFRP.Some achievements have been made in numerical simulation and experimental research of ECT of CFRP.However,deformation of ply due to impact is not considered in the existing computational model of computing EC response of CFRP.The model cannot meet the requirement for simulating ECT of CFRP in actual applications.Considering the ply deformation angle,this thesis deduces the conductivity tensor for describing the electrically anisotropic characteristic for the first time and proposes a general model for analysis of EC response of CFRP.The variations of eddy current(EC)in the ply and along the depth direction are studied.Study of ECT of fiber breakage and impact damage in multidirectional CFRP is performed by simulation and experiment.Fiber breakage is detected by the remote filed eddy current method(RFEC).Impact damage is detected by dual pancake coils.Scanning results show that the position and ranges of defects in ply can be judged by the variation of amplitude of voltage.No simulation and very few experimental research of ECT of sandwich structure have been done.Aluminum honeycomb sandwich structure is detected by two pancake coils.Domain decomposition method is adopted in the numerical analysis of ECT of aluminum honeycomb sandwich structure with ferrite-core coil.The upper panel,honeycomb core,lower panel,and ferrite core are placed in different subdomains.The simulation efficiency is greatly improved.Simulation results show that the distribution of EC in a subdomain is affected by ECs or magnetic current in the other subdomains.EC in ply flows mainly along the fiber orientation in the upper and lower panels.EC in the honeycomb core forms loop in the plane of core and vortexes in the walls of core.Numerical simulation and experimental research of C scanning of sandwich structure are conducted.Detection results with defects in the honeycomb core show that different kinds of defects such as core breakage,node debonding,core compression,and core wrinkle can be distinguished.The diameter of core compression can be assessed.Detection results with impact damage in the sandwich structure show that with increasing impact energy the deformation of core is more serious and the deformation area is increased.