Research On Phased Array Ultrasonic Non-destructive Testing Technique Of Carbon Fiber Reinforced Plastic

Carbon fiber reinforced plastic(CFRP)has the advantages of high strength,high rigidity,corrosion resistance and good designability,which can meet the requirements of light weight,high strength and heavy load required by special structures.CFRP has been widely used in aerospace,rail transit and other fields.Due to the complexity of structure design and manufacturing process,manufacturing defects are prone to occur during the manufacturing process.In addition,due to the inherent brittleness of the matrix and the relatively weak interlayer strength,impact damage is likely to occur when subjected to external impact loads.Manufacturing defects and impact damage will reduce the residual strength and service life of composite structures,leading to overall failure of the structure or other catastrophic consequences.Non-destructive testing and evaluation technique can provide characteristic information of internal damage of composite materials,which is an effective means for qualitative analysis and quantitative evaluation of manufacturing defects and impact damage.Phased array ultrasonic technique has the advantages of high resolution,high accuracy and good applicability to complex structures,and has received more attention in CFRP nondestructive testing.Aiming at the accurate detection and evaluation of CFRP manufacturing defects and impact damage,this paper carried out the research of phased array sound field modeling method,ultrasonic signal processing method and ultrasonic three-dimensional visualization imaging method of ultrasonic phased array non-destructive testing technique.Meanwhile,the experimental test verification of typical delamination defects and impact damage was carried out.The main research contents include:(1)Phased array ultrasonic sound field modeling and sound field characteristics analysis.First of all,aiming at the sound field modeling problem under the solid-solid interface of phased array ultrasonic,the phased array ultrasonic multi-point source three-dimensional sound field model is established based on the Rayleigh integration method.Then,the sound field characteristics are visualized and analyzed through model simulation,and the effects of active aperture and focus depth on the sound field focus depth,sound field focus area,main sound axis energy and other sound beam focus characteristics are studied.Finally,a detection parameter optimization method based on the sound field model is proposed,and experiment is executed to verify the method.(2)Research on ultrasonic signal processing method based on HHT.Aiming at the problem of accurate estimation of ultrasonic echo arrival time,an adaptive ultrasonic signal time-frequency analysis method based on Hilbert-Huang transform(HHT)is proposed.Firstly,the ultrasonic signal is decomposed by empirical mode,and the signal denoising and effective feature extraction are realized by screening the optimal intrinsic mode function.The arrival time of the ultrasonic echo is estimated through reconstructed signal envelope obtained by the Hilbert transform.the accuracy and anti-interference ability of the proposed method are verified through the arrival time estimation of the noise-added ultrasonic simulation signal.(3)Research on ultrasonic three-dimensional visualization imaging method based on defect depth information.In order to accurately identify the ultrasonic signal defect echo in ultrasonic signal,an adaptive defect threshold determination method based on the variance between classes is proposed to realize the adaptive identification of defect echo.Combining the ultrasonic echo arrival time estimation method and the defect echo identification method,an ultrasonic three-dimensional visualization imaging method based on the depth of the defect is proposed to realize the three-dimensional display of the defect spatial characteristics.In order to verify the feasibility and accuracy of the proposed method,phased array ultrasonic testing of the delamination defects standard sample is carried out,and the delamination defects are quantitatively evaluated using visualization imaging method.(4)Research on low-velocity impact damage characteristics of CFRP laminates.The phased array ultrasonic nondestructive testing method is used to accurately identify the impact damage characteristics of the CFRP laminates,and the characteristics of low-velocity impact damage and expansion methods is studied combining with the ultrasonic C-scan,the S-scan and the 3D image.The influences of impactor diameter on impact response parameters of the punch diameter,surface damage characteristics and internal damage characteristics are analyzed,and the correlation between them is studied.The correlation model between absorbed energy,pit depth and damage area under different impact parameters is established.The research content of this paper further optimizes the phased array ultrasonic non-destructive testing technology and methods,and realizes the intelligent assessment of internal defects and damage of composite materials.The signal processing algorithm improves the accuracy and efficiency of non-destructive testing and evaluation.The researc has important engineering practical value on optimizing the production process and guaranting operational safety of composites structures.