Research On Recurrence Analysis Of Ultrasonic Testing Signals For Carbon Fiber Reinforced Plastics

Carbon fiber reinforced plastics(CFRP)has been widely used in many fields like aerospace in a few decades,but the defects will inevitably grow during the manufacturing process.Ultrasonic nondestructive Testing technology has become one of the important means to detect defects of CFRP owing to its safety,harmless and versatility.However,the traditional ultrasonic attenuation method,which depends on the back-wall echo has limitation.To solve this problem,combined with Basic Scientific Research Project of Central University and Natural Science Fund Project in Zhejiang Province,a method of ultrasonic backscatter signal processing technology based on recurrence analysis provides a new idea for the ultrasonic detection technology of CFRP.The research work and achievements are as follows:(1)Analyze the status of ultrasonic testing technology for detecting the defects of CFRP,study the problem and limitation of traditional ultrasonic testing.Introduce the theory of ultrasonic propagation in CFRP and the components of the ultrasonic signal.The difficulties of ultrasonic detection of CFRP are summarized,and it’s proposed to use a new method of ultrasonic backscatter signal analysis based on recurrence analysis.(2)Study the algorithm of recurrence analysis and the steps of reconstruction of phase space,and research the selection of embedding dimension and the delay of time.The feature of recurrence plot(RP)are analyzed on macroscopic and microscopic.Recurrence quantification analysis(RQA)is introduced to quantitatively analyze the properties of recurrence.Analyze the feasibility of the method for detection of CFRP based on recurrence analysis in the view of nonlinear dynamic theory.(3)Apply the method of recurrence analysis to the ultrasonic testing signal processing of CFRP which have little porosity.Study the recurrence characteristics of ultrasonic detection signal with the effect of different defects.Realize the identification of the defects from far surface signal of thick section CFRP and the concentrated void defects of CFRP with little porosity.(4)A software of ultrasonic nondestructive testing has been developed based on LabVIEW and MATLAB including the functions of detecting signal acquisition,data storage and display,real-time signal processing which integrated Fourier spectrum analysis,HHT envelope spectrum analysis,wavelet time-frequency analysis and multi-scale recurrence analysis.The reliability of the software system was verified by ultrasonic testing of various typical defects.