Study On Nondestructive Testing Approach For Seam Defects Of Metal Materials Based On DCPD And PEC

Due to the harsh working environment,cracks in the large metal equipment often lead to accidents,so the health monitor to the key components of the equipment is of great significance.The seam defect is a kind of defect between the artificial defects and the natural crack,so the reseacch to the seam defects is a very important step to quantitative detection of the natural crack.At present,most of the the research for defect detection is focused on the single defect,however,several cracks usually occur in the same component,so the more attentions should be paided on the multiple cracks in the metals.Besides,a single non-destructive testing(NDT)method for global quantitative detection is hard to be carried out on large-scale metal components because of the limits of its characteristic signal,so it is an inevitable trend to promote the development of non-destructive testing technology to be systematic and automatic.Nondestructive testing technology(NDT)is one of the effective methods of structural health monitoring.For example,the localization test of overall defects can be easily realized by the direct current potential drop technology(DCPD)because its energy distribute in all parts of the tested equipment;the pulsed eddy current technology(PEC)has a unique advantage on the quantitative detection of defects because of its rich spectrum and fast response.In addition,DCPD and PEC are easily to reach automatic integration because they both belong to the electromagnetic method of NDT,which has remarkable potential in engineering application.Based on mentioned above,the research work mainly focuses on the following three aspects:(1)The research on the defects' localization appraoch by DCPD.Firstly,the finite element simulation models of DCPD and ACPD are established,and the influence of dimension and location of defects as well as testing site are analyzed,which provide reference for the experiment study.Then the platform of DCPD is established and experiments are carried out.The experiments verify the simulation results well.Finally,an approach to measure the locations of the multiple defects in the metal is proposed based on DCPD.(2)The research on seam defects' quantitative test by PEC.On one hand,the numerical model of PEC is established,and the model is optimized from the aspects of meshing strategy and boundary conditions.On the other hand,the experimental platform of PEC is designed and its detection ability is evaluated.Then the relationship model between the electromagnetic signals and the depth of defects is put forward based on the simulation and experiment.Finally,a quantitative detection approach of seam defects is proposed.(3)The research on the fusion nondestructive testing approach for the multiple defects detection in the metal component based on DCPD and PEC.The interface of DCPD and PEC is designed based on the VB,and motion control program is completed to develop the DCPD-PEC fused NDT system.Then the localization and quantification detection of the seam defects of 7075 aluminum alloy materials was carried out based on the system.Finally,the solution to reduce the error was discussed.