Real-time On-line Cure Monitoring Of Composite Repair By Electromechanical Impedance Technique

Metal structure has the advantages of mature design,easy processing and low cost.It is widely used in aerospace,civil engineering and many other industrial fields.It is one of the most common and important structures.Whether it is the Hong KongZhuhai-Macao Bridge,the Shanghai Tower,the"Fighting" all-sea deep manned submersible,the C919 large passenger plane and the China Space Station,they can all be seen.For a long time,the fatigue,corrosion,load and changes of the working environment of metal structures have been the main factors causing structural failures and have severely restricted the service life of metal structures.In order to ensure the safety and reliability of the structure,restore its carrying capacity,and extend its service life,composite material patch technology provides an effective solution.In this paper,a curing monitoring method based on electromechanical impedance method is developed,which comprehensively utilizes the changes of electromechanical impedance signal and extracts multiple key curing indexes.It is verified through experiments that these key curing indexes have better characterization effects than traditional curing indexes.In order to prove the test results,a dielectric resin curing tester(DEA)was used to measure the precise curing curve of the same specimen,and it was compared with the key curing index curve based on the electromechanical impedance signal to achieve a strong consistency.After accurate comparison with the DEA curve,each stage of the curing reaction can be judged through the key curing index curve of the electromechanical impedance,so as to realize the online real-time monitoring of the composite patch repair structure.The main contents of this paper are as follows:(1)Perform statistical classification of typical composite repair structures and repair methods,simplify the more complex repair structures in actual engineering applications to composite material patch-flat metal aluminum plate structure;characterize the characteristics of the repair structure curing monitoring in the experimental environment,Make test pieces of composite patch repair structure.(2)According to the possible working conditions in the actual application of the project,two repair methods,dry repair and wet repair,can be used.In order to meet the monitoring requirements,two sensor layout methods are selected.One is to paste the piezoelectric ceramics on the surface of the composite material patch,and the other is to weld the piezoelectric ceramics to the embedded structure in the smart sandwich.The two sensor layout methods correspond to two different composite patch repair technologies,and both have a small impact on the structural performance.(3)Collect the electromechanical impedance signal of the composite material patch repair structure specimen during the curing process,extract the signal characteristics,and propose a number of key curing indicators,and process the data to characterize the relationship between the signal and the curing degree and curing rate.Compared with the commonly used classic indicators,the key curing indicators proposed can circumvent the limitations of the test environment and can more effectively characterize the curing characteristics.(4)Verify the proposed curing monitoring technology based on electromechanical impedance.For the bonding structure of composite materials and metals,make suitable test pieces,and use the electromechanical impedance method(EMI)and dielectric curing analysis method(DEA)to compare the same composite The curing process of the material patch repairing the structure test piece is simultaneously monitored in real time.The verification test shows that the key curing index curve of the electromechanical impedance method is consistent with the curing curve of the DEA test,which can effectively realize the real-time monitoring of the curing process of the composite repair structure under laboratory conditions.