Study On Characterization Of Defects In CFRP Using Ultrasonic Imaging Testing

Carbon fiber reinforced polymer composite materials are widely used in aerospace and military industries due to their low relative density,specific strength and specific modulus,making their reliability and safety requirements increasingly high.Ultrasonic testing is a common technique for the detection of carbon fiber composite materials.For carbon fiber composite workpieces,how to improve the accuracy and automation of imaging detection is an in-depth study.In this paper,combined with the actual requirements and development process of carbon fiber composite ultrasonic imaging detection system project,the key technologies such as detection methods,system software design,signal processing and defect identification analysis in ultrasonic imaging detection are deeply studied.The main work and innovations are as follows:First of all,the sound field analysis of the ultrasonic probe is performed by the mathematical model of the ultrasonic transducer sound field.It is found that the intensity of the sound beam diverges with the increase of the width of the ultrasonic probe,and the high-directional sound beam emitted by the ultrasonic probe with a large width.The paraxial approximation of the wavelength can be well satisfied.The acoustic beam focusing simulation of the ultrasonic transducer is performed by using a mathematical model of the velocity source uniformly distributed along the boundary within the radius R₀.The amplitude of the sound pressure gradually increases in the positive z direction until the gathering point reaches a maximum value and gradually appears Decreasing trend,when the sound beam gathering distance is far away from the near field region of the ultrasonic probe,the accumulation of sound beam energy cannot be achieved.Secondly,the virtual instrument structure and templated design concept are used to develop and build a set of ultrasonic imaging detection system to realize the two-dimensional motion scanning detection function of carbon fiber composite test pieces,real-time ultrasonic signal acquisition,processing,analysis and imaging,for subsequent Provides a basis for imaging detection of internal defects in carbon fiber composites;Then,study on the ultrasonic imaging test and imaging method of delamination defects and impact damage defects in carbon fiber composites.By measuring the ultrasonic A-scan signal of the layered defect and the impact damage defect at different positions,the gate of the A-scan signal is set to extract the amplitude and depth information as an ultrasonic scan imaging detection image that characterizes the defect signal feature to construct the defect.The results show that the ultrasonic imaging detection system can realize the imaging detection of the internal defects of carbon fiber composites.Finally,the-6dB method and bilinear interpolation are used to quantitatively analyze the defects,which effectively improves the error of quantitative analysis of defects.Finally,the problem of inaccurate positioning and large quantization error in the low-energy impact damage quantitative detection process is studied for the-6dB method.The image of the defect image is sharpened based on the Laplacian image,and the pixel contrast of the defect area and the background area is improved to enhance the defect image.The image segmentation algorithm based on K-means clustering is adopted for the enhanced image.Image segmentation can segment the edge of the image of the more continuous defect area and extract the contour information of the defect area more accurately.By analyzing the segmented defect image based on the connected region,the segment features of the connected region pixel sum and compactness are used for filtering and culling.Through image enhancement,segmentation and connected region analysis and processing,the location and recognition of defect regions in the detection of impact energy 2J and 4J are realized,which improves the accuracy of defect location and reduces the error of defect quantization.