Research On Composite Delamination Defect Detection Based On Phased Array Laser Ultrasonic

Carbon fiber composite has the advantages of light weight,high specific strength,better thermodynamic performance and low cost,which plays an irreplaceable role in reducing structural quality and improving product performance.It is an ideal structural material in the field of aerospace.In the process of manufacturing and service stages of carbon fiber composites,lamination defects are easy to occur,which will damage the mechanical properties(compression strength and stiffness)of the materials,and even lead to the fracture of the composites in serious cases.This paper aims at the high-precision and efficient identification of delamination defects as the core problem of carbon fiber composite material delamination defect detection,based on the actual development process of the phased array laser ultrasonic inspection system,and the key technologies have been studied in depth such as finite element model of phased array laser ultrasonic experimental principles,ultrasonic signal analysis of delamination defects,and feature extraction and recognition of defects.The main contents and conclusions of this paper are as follows:(1)The finite element model for phased array laser ultrasonic testing of delamination defects in carbon fiber reinforced composites was established.Three equivalent force sources were used as laser sources in the model.The phased array excitation was realized by delaying 0.2 ?s for each laser source.At the same time,the characteristics of twodimensional transversely isotropic plate were introduced to establish the model of carbon fiber composite laminate.Based on the model,the influence of different laser sources,different depth and size of delamination defect and different distance between laser source and delamination defect on ultrasonic field are studied.The evolution law of sound field containing multiple delamination defects is discussed,which provides theoretical basis for laser ultrasonic experiment.(2)This paper studies the time-frequency analysis methods suitable for composite detection signals,including short-time Fourier transform(STFT),continuous wavelet transform(CWT)and Hilbert-Huang(HHT),and carries out MATLAB simulation respectively.The results show that Hilbert Huang transform has the advantages of high resolution,more accurate local feature analysis and strong adaptability compared with the other two methods.According to the advantages and disadvantages of adaptive noise complete empirical mode decomposition(CEEMDAN),an improved CEEMDAN decomposition method based on extremum extension is proposed to solve the problems of end effect and mode aliasing in empirical mode decomposition(EMD).The simulation results show that the IMF component efficiency of the improved CEEMDAN decomposition method is better than that of other EMD decomposition methods,it can better suppress the end effect and modal aliasing.(3)The defect feature extraction and recognition method based on composite detection signal is proposed.Firstly,the defect sensitive mode component(IMF)is selected based on the improved ceemdan decomposition algorithm,and then the local characteristics of the sensitive IMF are obtained through Hilbert transform(HT).Finally the delamination defects are deeply quantitatively analyzed and identified according to the IMF components and two indicators(instantaneous frequency and instantaneous amplitude).The results show that the improved HHT time-frequency method has higher accuracy and identification degree for feature extraction and recognition of delamination defects.Compared with the traditional time-domain analysis,the maximum error of defect depth quantitative analysis is reduced from 39% to 20%,respectively,and the improved HHT time frequency analysis method can accurately identify different sizes of delamination defects.(4)A set of phased array laser ultrasonic testing platform is set up.The P-wave reflection method and P-wave transmission method phased array laser ultrasonic detection are realized in the form of multiple excitation and single receiving.The defect transmission amplitude and defect reflection amplitude after focusing are obtained in principle.The results show that the defect amplitude of phased array laser source is 1 ? 2 times stronger than that of single beam laser source.