A Research On Ultrasonic Evaluation System Of Material Defects In Carbon Fiber Reinforced Polvmer

With the wide use of carbon fiber reinforced plastics,the significance of non-destructive testing(NDT)technology has become increasingly prominent.Non-destructive testing technology is an important means of product quality control,which can detect internal defects directly without damaging the tested object.Besides,NDT technology can be used in all manufacturing stages of the product.However,the traditional composite ultrasonic non-destructive testing method deeply relies on the back-wall echo,which limits the application of ultrasonic non-destructive testing in NDT area,especially for complex shapes and thick-section CFRP components.This paper focuses on the ultrasonic signal processing of CFRP,and a new method of ultrasonic testing technology for CFRP based on recursive analysis is proposed,and the effectiveness of the method is verified by experiments.The main contents are as follows:(1)Analyse the current condition and deficiencies of ultrasonic testing technology for CFRP defects,and study the features and application scopes of various ultrasonic non-destructive testing methods.On this basis,a defect detection method of carbon fiber composite based on ultrasonic backscattering signal analysis is introduced,and the backscattering signal is deeply studied and analyzed.(2)Study the theory of recursive analysis,and establish the relationship between recurrence plot and material defects.According to the nonlinear characteristics of ultrasonic wave propagation in CFRP,the ultrasonic non-destructive testing technology of CFRP as well as structure observation,the recursive analysis of ultrasonic detection signal and the method of defect feature extraction are studied,and an ultrasonic non-destructive testing method for CFRP based on recursive analysis of ultrasonic backscattering signal is proposed.(3)In order to obtain the information in the detection signal more accurately,the recursive quantitative analysis method is introduced.The feasibility of recursive analysis for ultrasonic non-destructive testing of carbon fiber composites is verified by means of standard blockers of carbon fiber composites,and two basic recurrence quantification analysis indexes are studied:the determinism rate(DET)and the recurrence entropy(ENTR),and the relationship between the porosity and the quantitative parameters of tested CFRP component is obtained by curve fitting method.Furthermore,the unknown carbon fiber test block is detected by using the evaluation index,and the results of the metallographic observation are compared to verify whether the recursive analysis could be effectively used for the detection of carbon fiber composite defects.(4)Develop a set of ultrasonic non-destructive testing software.The method of joint development between MATLAB and Lab VIEW is studied,and the ultrasonic test system software is developed.The software not only includes the basic functions of detecting signal acquisition,display and data storage,but also has many kinds of detection signal processing functions such as wavelet time-frequency analysis,spectrum analysis and recursive analysis.