Study On Key Techniques Of Ultrasonic Nondestructive Testing Composite Parts

Composite material has been widely used in aerospace, military, automotive and otherfields because of its superior performance. Various types of defects may be appeared in theprocess of composite material component production-manufacturing and using. Thesecurity of components is greatly reduced, therefore it is very necessary to take effectivenondestructive testing methods.This paper studies some key techniques of ultrasonic nondestructive testing fiberreinforced resin matrix composite material structures. Firstly, the rule of wave propagationin anisotropic composites is studied. Computer simulations are carried out according toeffective detection model and further the correctness of the model is verified by means ofspecific experiments measurements. Secondly, in the field of air-coupled ultrasonic testingtechniques of composite material, the characteristics of coupled transducer acoustic andattenuation factors of detection are studied, and then a method for detecting compositematerial component with high pressure gas coupled is proposed. Sensitivity compensationprinciple for variable thickness composite material component detection is studied and thenverified experimentally. Finally, the changes of beam shape for surface component testingand principles and methods of tracking transducer scanning trajectory on curved profile arestudied. Then hardware and software systems are designed. Twin-robots compositeautomatic ultrasonic testing system that has better function and higher performance isdeveloped, and experimental applications research is carried out.In the first chapter, the purpose and significance of this paper is described. Relatedresearch at home and abroad is summarized and analyzed for non-destructive testingtechniques of composite materials, ultrasonic testing simulation, time-frequency analysismethods of ultrasonic signal, air-coupled ultrasonic inspection technology andcomplex-shaped profile member of ultrasound ultrasonic testing technology. Finally, thecontents of the thesis is outlines.In the second chapter, propagation rule of ultrasonic for anisotropic compositematerials is studied. Based on the knowledge of anisotropic medium, acoustic fields distribution of ultrasonic within the composite material is studied by using Multi-Gaussianbeam model. The simulation results of sound field axial section and radial distributionplanning surface of water-composite materials-water interface are given and analyzed.Based on the simulation results of transmission acoustic field, experiments on transmissionacoustic field for different materials (carbon fiber and glass fiber composite materials) andthickness specimens are carried out. The best position of received transducer for actualtesting is proposed according to comparative analyzing experimental results and simulation.In the third chapter, some time-frequency analysis methods of ultrasonic signal arestudied, including STFT, wavelet transform and WVD. The analysis method of HHT ismainly studied, including IMF, EMD and Hilbert spectral analysis. HHT is applied toanalyze defect echo signal for composite materials with ultrasonic testing.In the forth chapter, the application of air-coupled ultrasonic testing to compositematerials testing is studied. According to analyzing acoustic field characteristic ofair-coupled transducer, simulation and experiment results of acoustic field of air-coupledultrasonic transducer are given. A method for improving accuracy and sensitivity ofdetection by increasing the pressure of detecting environment (that is, increasing the densityof the gas coupling in detection environment). The testing system of air-coupled ultrasonicinspection is constructed. The concrete test results of composite components is given byusing of surface reflection and transmission methods.In the fifth chapter, the key techniques of ultrasonic nondestructive testing forcomposite structures with complex shaped profile are studied. Errors that prone to appear inthe process of detection for composite components which thickness have continuous andmutation changes are analyzed. The method of sensitivity compensation is proposed, andthen specific detection results for the application of this method are given. Secondly, whentransmission method detecting curved (convex, concave) composite components, soundfield distribution of three media (water-composite-s-water) with different curvatures issimulated by using of multi-Gaussian beams model. Sound field distribution of the axialand radial cross-section is studied, and then verification experiment is given. Finally, theprinciple of ultrasonic transducer to curved profile by using twin-robots equipped is studied,and the path of scanning trajectory tracking is also studied. In the sixth chapter, based on the results of detection analysis of composite structureswith complex shaped contour, twin-robot automatic ultrasonic testing system is developedand the framework of hardware structure is built, including multi-joints robot and itscontroller, pulse meter transceivers, high-speed A/D data acquisition card, cabinet, etc.system software is compiled based on VC#, module includes data acquisition, robot motioncontrol, automatic scanning imaging and data processing module. Automatic ultrasonictesting system is applied with twin-robot. Experiment on synchrony of twin-robots inscanning trajectory is carried out. Subsequently experiment on ultrasonic automaticscanning of composite components with various cylindrical and curved shape is carried out.Identification ability of system on different shapes and defects is qualitatively analyzed,furthermore delectability of system on different types of defects is qualitatively analyzed.