Research On Damage Detection Of Carbon Fiber Composites Based On Acoustic Emission

Composite materials are susceptible to processing parameters in the preparation process,resulting in point defects,dislocation defects and surface defects.During the process of usage,damages such as surface distortion,irregularities,delamination,degumming,perforation and cracks may occur due to external forces,which seriously affect the performance of material components.This thesis mainly focuses on the problem of damage detection of carbon fiber composites,carried out the damage mechanism of carbon fiber composite materials,the signal characteristics of acoustic emission signals generated during the damage process,the location of material damage sources,and the identification of material tensile damage,etc.The main contents are as follows:The first part of this paper deals with research on defect and damage identification technology of carbon fiber composites.The defects and damage mechanisms of carbon fiber composites were studied,the current damage detection methods were analyzed,and the existing problems were summarized.The working mechanism of acoustic emission detection technology is studied,and the current application in various industries is analyzed.The damage source localization and damage source identification methods of carbon fiber composite materials are studied,and the advantages and disadvantages of the acoustic emission detection instrument in the detection process are analyzed,and the importance of designing a full-waveform acoustic emission detection instrument is proposed.Secondly,a fullwaveacoustic emission detection scheme is given.Aiming at the problem of signal data compression and simplification in current acoustic emission detection instruments,a design scheme for full-waveform acoustic emission detection is proposed,and a full waveform acoustic emission detection system is developed,at the same time the system performance verification and testing were completed,the complete collection of acoustic emission signal data was achieved,it is further applied to the research of tensile damage detection of carbon fiber composites.Thirdly,the analysis and research of acoustic emission signals of carbon fiber composites are conducted.A threshold-optimized wavelet denoising method is studied,as a result of a problem that the collected signal is mixed with a lot of noise and affects the accuracy of the detection result,in the process of correct acoustic emission detection.The characteristics of acoustic emission signals of different spectrums is studied,based on the signal decomposition and reconstruction methods,so the characteristics of the acoustic emission signals of carbon fiber composites during the damage process were obtained.A K-means clustering method based on genetic simulation initialization algorithm optimization was proposed,in order to achieve effective clustering of acoustic emission parameter signals to realize effective clustering of acoustic emission parameter signals.A carbon fiber composite plate positioning model was established by using the wavelet neural network modeling method,to be identifiedthe recognition of unknown signals.Fourthly,damage source localization of carbon fiber composite board is developed.The Lamb wave propagation models in isotropic materials,single-layer composite materials,and multilayer composite plate structures are obtained,and reveal the propagation characteristics of Lamb waves in different structures,bystudy on propagation characteristics of Lamb Waves in different materials.The propagation characteristics and propagation modes of Lamb waves in carbon fiber composite materials are studied,and the feasibility of accurately locating damage sources of carbon fiber composite plates by Lamb waves is demonstrated.In order to obtain the propagation speed of Lamb wave in carbon fiber composite plate,the propagation speed of Lamb wave in different directions of carbon fiber composite plate is measured experimentally,and the relationship between the wave velocity and the angle of carbon fiber is fitted.In order to accurately locate the acoustic emission source of carbon fiber composite board,a location algorithm based on Lamb wave for acoustic emission source utilizing four-sensor is proposed.In order to achieve accurate localization of unknown damage sources,a wavelet neural network was established,and a localization model of acoustic emission sources was established for fast and accurate localization of damage sources of carbon fiber composite plates.Lastly,research on tensile damage identification of carbon fiber composites is carried out.The mechanical properties and strength criteria of composite are studied,and a method for establishing a damage identification model of carbon fiber composite panels by using acoustic emission signals generated during the damage process is proposed,because of the composite material strength analysis method,there are problems such as complex application and low reliability of the analysis results.The parametric analysis,spectrum analysis,and wavelet analysis were used to carry out the research,and the purpose was to conduct a multi-angle investigation on the tensile damage identification of carbon fiber composites.The evolution law of acoustic emission parameters over time is summarized,based on the analysis of the characteristics of acoustic emission signal parameters.The correspondence between the damage signal and the damage category are obtained,in connection with the cluster analysis of tensile damage signal parameters.A damage recognition model was established based on BP neural network,in order to realize the accurate recognition of unknown damage signals.Carry out time-domain analysis and research on acoustic emission signals during damage,and the evolution of signal energy over time during tensile damage is developed,and a wavelet and wavelet packet analysis tool is proposed for the study of damage signals.