Detection Of Impact Damage Of Composite Laminates Using Vibro-Acoustic Modulation Detection Technology

Composite materials have been widely used in aerospace,transportation,automobile manufacturing and other fields due to their corrosion resistance,fatigue resistance,and easy to integral molding.Carbon fiber reinforced plastics(CFRP)is one of the most mature and widely applied composite material in aerospace field.Its superior performance makes it a preferred material for main bearing structures.However,during the manufacture,service,and maintenance of CFRP,the damage will be caused by its manufacturing process and external factors,which will affect the integrity and service life of the structure.Low velocity impact damage,as a common defect in composite laminates,visual inspection is not obvious,but such damage will have a great impact on the strength and mechanical properties of the structure,causing potential safety hazards for in-service components.Therefore,it has been paid attention to how to quickly and highly sensitive the non-destructive testing and evaluation of composite laminate structures.This study mainly carries out the research on the vibro-acoustic modulation detection technology of CFRP laminates,and explores how to identify and evaluate the impact damage in carbon fiber composite materials quickly and effectively.Firstly,describes the basic principle of nonlinear ultrasonic,analyzes the sources of different nonlinear effects in nonlinear ultrasonic,From the one-dimensional wave equation of isotropic body,the nonlinear ultrasonic dynamic equation and its approximate solution are deduced.Furthermore,deduced the expression of the solution of the nonlinear wave equation in the structure.Based on the existing vibro-acoustic modulation model,the Modulation index MI is defined to evaluate the degree of damage.Secondly,A three-dimensional finite element model of CFRP laminates is established,and the natural frequencies and vibration shape of the composite laminates were obtained.The influence of the frequency and amplitude of the low-frequency vibration signal and the high-frequency ultrasonic signal on the experimental results of the vibro-acoustic modulation detection experimental was analyzed,and the experimental parameters were optimized.The complex Morlet wavelet cluster envelope demodulation method is applied to the processing of vibro-acoustic modulation detection experimental signals.By constructing a complex Morlet wavelet cluster with band-pass filtering characteristics,the filtering and demodulation links of the traditional mechanical fault diagnosis and demodulation method are combined to realize the integration of filter and demodulation.The demodulation index DI is defined by analyzing the principle of complex Morlet wavelet envelope demodulation and the confirmatory simulation experiment.The results show that using the demodulation index DI can reduce the computational complexity and realize the rapid analysis of data.Based on the above numerical simulation and experimental research,the experimental research on vibro-acoustic modulation detection of composite materials with low velocity impact damage is carried out,The natural frequency and vibration shape of CFRP laminates are obtained by dynamic response test,and the basic parameters of the vibro-acoustic modulation detection experiment are determined.The corresponding low-frequency vibration and high-frequency ultrasonic frequency are selected to detect the 13.9J and 7.09 J impact damage samples and the reference samples.The influence of low frequency excitation voltage on the modulation effect is analyzed,using the applied mathematical statistics and the complex Morlet wavelet cluster envelope demodulation method,the modulation index and demodulation index are analyzed with the increase of the low-frequency excitation voltage.The experimental results show that vibration mode selection is very important in the vibro-acoustic modulation detection,When the low frequency excitation voltage is large and the vibration shape is selected reasonably,the modulation index and demodulation index of the damage sample is increased rapidly with the increase of the low frequency excitation voltage,and can effectively identify the reference sample and the defect sample.In the evaluation of vibro-acoustic modulation detection technology,the modulation index increases approximately linearly with the increase of low-frequency excitation voltage,which is suitable for quantitative evaluation.The linearity of the modulation index is better than the demodulation index,but the solution speed of the demodulation index is superior to the modulation index,and it can quickly determine whether there is damage in the laminate.