Research On Ultrasonic Imaging In CFRP Based On Compressed Sensing

Carbon Fiber Reinforced Plastic(CFRP)has the advantages of low relative density,large specific strength and specific modulus,and is widely used in aerospace,automotive,marine engineering and other fields.CFRP is prone to various defects during production and service,which seriously affect their mechanical properties and bring hidden dangers to safety applications.Numerous studies have shown that ultrasonic testing can effectively detect delamination defects and impact damage in composite materials,but the large amount of data generated during the detection process and the low detection efficiency seriously hinder the application of ultrasonic testing.Based on the analysis of the theory of compressed sensing and the characteristics of ultrasonic detection imaging,this paper studies the delamination defects and impact damage ultrasonic imaging methods of CFRP based on compressed sensing.The main research contents and innovations are as follows:Firstly,the theory of ultrasonic testing is studied.On this basis,a set of ultrasonic automatic detection and imaging experimental system is built.The system is mainly composed of ultrasonic testing instrument,3-D motion control platform and upper computer software.It can reliably collect ultrasonic A-scan signals and effectively construct ultrasonic C-scan images with delamination defects and impact damage by extracting the amplitude of the defect wave.Experimental studies found that ultrasound image quality is closely related to scan step size and signal sampling rate.Therefore,in order to ensure the image quality,the traditional ultrasonic imaging detection method is used for delamination defects and impact damage imaging,which has the disadvantages of low detection efficiency and large data volume.Secondly,the method of delamination defect and impact damage ultrasonic imaging based on compressed sensing theory is studied.Aiming at the problem that the conventional ultrasonic detection improves the image resolution and contour representation accuracy by increasing the number of sampling points,the detection and imaging of ultrasonic A-scan signals based on compressed sensing is proposed.The results show that only 30% of the A-scanning defect wave signal can obtain image quality similar to that of full sampling.In order to improve the imaging efficiency of C-scan,an ultrasonic C-scan imaging based on compressed sensing is proposed.The results show that compared with the traditional ultrasonic C-scan imaging method,the compressed sensing imaging method combined with A-scan and C-scan can significantly improve the detection efficiency and reduce the data sampling and storage.Finally,for high-quality ultrasound images occupying a large space,which is not conducive to preservation and transmission,the ultrasound image compression and reconstruction method based on compressed sensing theory is studied.Experimental studies have been carried out from both the spatial and frequency domains of the ultrasound image.The results show that the quality of the ultrasound image reconstruction based on the spatial domain is affected by the wavelet base and the observation matrix.The ultrasonic image reconstructed by sym4-Hadamard method is superior to the ultrasonic image reconstructed by haar-Bernoulli method in both resolution and contour representation.In addition,the frequency domain-based superresolution reconstructed image quality is significantly better than the spatial domainbased ultrasound image reconstruction quality.The frequency domain-based ultrasound image reconstruction method uses only 0.1 compression ratio to obtain reconstructed images with almost no difference in resolution and defect contour representation compared with the original image.This provides a feasible method for the compression preservation and transmission of delamination defects and impact damage ultrasound images.The work of this paper provides a theoretical basis for delamination defects and impact damage ultrasonic imaging of CFRP based on compression sensing,and has certain theoretical and practical value.