Quantification Of Damage In Composite Plates Based On Ultrasonic CT Images

Due to its excellent performance,laminated composite materials are widely used in various fields such as aerospace,engineering equipment,automotive and shipbuilding industries.However,during production and long-term service life,composite components may suffer from various degrees of damage due to environmental factors such as stress impact,expansion compression and temperature changes.These damages often occur inside the component where they cannot be seen.If the internal damage of the composite material is severe enough,it may cause serious catastrophic accidents in extreme cases.Therefore,regular structural health monitoring of laminated composite components is crucial.Lamb wave is one of the unique ultrasonic guided wave forms in flat thin plate materials.It has been widely used for structural health monitoring of composite materials due to its characteristics such as long propagation distance,low attenuation rate,good detectability and sensitivity to various small damages.Although many advances have been made in Lamb wave-based damage imaging technology,the accuracy of imaging is often poor due to problems such as frequency dispersion effect,boundary superposition effect,mode mixing,and requiring baseline signals for auxiliary judgment which makes it difficult to obtain accurate information about specific location,shape and size of damages.As a result,theoretical analysis,simulation,and experimental validation are used in this paper to carry out the following work.(1)The thesis systematically introduces and derives the basic principles of Lamb wave propagation in composite plates,and obtains the dispersion equation and dispersion curve of Lamb waves based on the theoretical derivation;it provides the theoretical basis for the selection of suitable Lamb wave modes and frequencies and the reduction of anisotropy of Lamb wave propagation in composite plates in the later paper.(2)A method based on Continuous wavelet transform(CWT)to compensate the peak point offset and extract the Time-of-Flight(TOF)of Lamb waves in composite plates is presented.The theoretical basis of ultrasonic Lamb wave laminar imaging based on Filtered Back-Projection(FBP)is introduced,and the TOF data obtained based on CWT is substituted into the FBP imaging algorithm as the projection value to derive an ultrasonic CT composite plate damage reconstruction imaging algorithm based on the Fourier center slice theorem.(3)A dual-scale morphological filtering-based image noise reduction algorithm was investigated for noise reduction and optimization of FBP damage reconstruction images.The proposed dual-scale morphological filtering method alternately filters the image by two morphological structure operators at different scales to remove large artifacts and noise in the image while ensuring the continuity and integrity of the damage edges.(4)A method for quantifying damage of composite plates based on the FBP damage imaging algorithm,dual-scale morphological filtering algorithm,Canny edge detection algorithm and convex packet detection algorithm of ultrasonic CT images is proposed.Its work can image and quantify the damage of the composite plate,including giving information on the specific location,shape and area of the damage of the composite plate,so that the damage of the composite plate can be quantified visually and the severity of the damage can be understood.(5)The proposed method of quantifying the damage of composite plate based on ultrasonic CT images was verified by numerical simulation with Abaqus 3D finite element simulation software.Based on the analysis of the finite element simulation,the propagation of the A0 mode of Lamb wave in the composite plate was firstly investigated based on the point force method,and the circular and elliptical damage models were set up by the volume splitting method to obtain the TOF data of the composite plate under different damage setting conditions of Lamb wave,and the data were substituted into the FBP imaging algorithm to obtain the damage reconstruction images of different locations and shapes results.Based on the damage reconstruction results,the effects and damage quantification results based on the dual-scale morphological filtering and the rest of the traditional filtering methods are compared,and the feasibility,accuracy,superiority and reliability of the proposed method are demonstrated.(6)The feasibility,reliability and accuracy of the proposed method were further verified by real composite plate delamination damage quantification experiments.The experimental results match with the finite element simulations,indicating that the proposed study on damage quantification of composite plates using ultrasonic CT images is feasible and accurate.The research results of this paper have some engineering applications for visualizing structural health online monitoring and damage information detection,extraction,imaging and quantification in carbon fiber composite panels using ultrasonic Lamb.