Study On Key Techniques Of CFRP Digital Ultrasonic Inspection System

Carbon Fiber Reinforced Plastics (CFRP) was widely used in the aeronautic,astronautic and arms industry and so its reliability and security become more and more important. Ultrasonic inspection which takes a crucial position in products quality control is the regular technology for CFRP test. For the CFRP parts, how to improve precision and degree of automation is a problem that need deeper research. Combined with the actual requirement and developing process of CFRP Ultrasonic non-destructive inspection project, some key techniques such as inspection method, signal processing, flaw analysis, void content test and software design are deeply studied in this thesis.In chapter 1, the signification of research work of this thesis was discussed. The developing status of relative technique such as CFRP Ultrasonic non-destructive inspection,void content test, ultrasonic scan and imaging means, ultrasonic signal process, ultrasonic C-scan image process were analyzed.In chapter 2, the automatic ultrasonic inspecting method for curved surface part was studied. Firstly, the basic theory of ultrasonic inspection technique was introduced, then based on ultrasonic measure, curved surface modeling, scanning path planning and ultrasonic scan imaging, the all-in-one system of inspection was constructed. On the basis of robot theory, the kinematic model of multi-freedom ultrasonic inspecting robot for curved surface parts was set up. Finally, the kinematic equation and result of five-freedom ultrasonic inspecting system were presented.In chapter 3, the flaw wave position-finding technique of curved surface and depth-changeable parts was researched. Depict the basic theory of wavelet transform, including concept and algorithm realization of continuous wavelet transform, physical meaning of discrete wavelet transform, multi-resolution analysis and Mallet algorithm. A flaw wave position-finding technique based on complex wavelet transform was proposed. Wavelet transform was used to draw contour feature wave of ultrasonic radio signal, then found the position of all echo wave by continuous-point threshold algorithm, finally decided the peak and position via surface wave and bottom wave. It is shown that method of wavelet process can find the peak and position of flaw wave accurately.In chapter 4, the flaw analysis method of ultrasonic C-can image was studied. Proposed a method that segregated flaw area from image by means of threshold segment and area label algorithm, then edge-track algorithm was used to draw the edge of flaw area, geometrical parameter system was built to depict and recognize flaw. The imaging method of ultrasonic C-scan was studied, the threshold-deciding method of image segment was offered by the principle of error probability minimum. Then the concept and algorithm of flaw area labeling was presented, edge operator and edge-track algorithm were employed to draw the flaw edge from C-scan image. The geometrical parameter of flaw area was calculated. It is shown that the parameter system can describe the feature of flaw area well and so redound to works of flaw recognition further.In chapter 5, A portable ultrasonic inspecting system for void content of CFRP was developed. The mathematic model to test void content of CFRP was studied and the formula between void content and ultrasonic attenuation coefficient was established. Based on ultrasonic echo method, the relation between ultrasonic attenuation coefficient and the amplitude of surface as well as bottom echo wave was studied, and portable ultrasonic inspecting system for void content of CFRP was constructed. In order to acquire the position data of probe in the testing system, an method of mapping an optical mouse into a virtual position sensor was proposed. The lower filter driver for optical mouse was programmed, which can intercept the report descriptor and I/O interrupt requires of the mouse. An installation program was made to set up filter driver into operating system of computer. User application accessed this device and read its report descriptor to obtain the position information needed for testing system. It is shown that the result of developed device is accurate so it can all-sided evaluate void content status of CFRP.In chapter 6, Software design of ultrasonic imaging system for CFRP was researched. Classification standard and internal structure of software capability maturity model(CMM) were introduced and the realizing method and key process of CMM in CFRP ultrasonic test system software were studied. The practice of layered design method in software system general design was depicted and discussed the rype,trait and form of data in the software system. General function structure of CFRP software system was described. The realizing method of two key technique like combined imaging and report output in the system was offered.Finally, main result of the thesis was summarized, the prospects and further research work were presented.