Research Of Nonlinear Ultrasonic Detection Technique Based On Harmonic Theory And Beam Mixing

With the development of material design and process technology, metal materials and its bonded structures are widely used in aerospace, automotive, shipbuilding, machinery manufacturing and other fields. However, because of the influence of formation process and working environment, It is more prone to appear early degradation of the mechanical properties in metallic material and its bonding structure. Nonlinear ultrasonic testing technology with its high detection sensitivity is used in the detection of material microstructure and interfacial adhesion strength. But there are still many problems in terms of mechanism analysis, study of test methods and signal processing about the technology. Therefore, this study has important theoretical and practical significance to effective evaluation of characteristics of metal materials and its bonded structures, and to application and promotion of nonlinear ultrasonic testing technology.Steel- steel interfacial bond strength is tested based on the theory of harmonic; Nonlinear space distribution of steel and LY12 alloy are detected based on the theory of beam mixing; The test results are analyzed and discussed.Firstly, finite amplitude method is selected to detect interfacial bond strength and non-collinear beams mixing method is selected to detect the microstructure of the material in consideration of the features of detecting objects, engineering practical outlook and experimental principles and experimental apparatus of two methods.Secondly, nonlinear generation process is analysized when the ultrasonic wave propagates in the bonding interface. The relation between adhesive strength and nonlinear effects of ultrasound is established. The nonlinear parameter A₃/（A₁A₂）is measured at different excitation voltage based on Ritec SNAP nonlinear ultrasonic testing system. The results show that the relationship between nonlinear parameter and bonding strength is monotonic.Finally, the non-collinear beams mixing ultrasonic testing platform is set up. Non-linear response of steel and LY12 aluminum alloy is compared. Nonlinear space distribution of LY12 aluminum alloy which has significant non-collinear non-linear response is further studied. The mixing wave signal which contains noise is made reduction processing using wavelet packet decomposition technique. The results showed that:（1） Compared with steel specimens,LY12 aluminum specimen has stronger non-linear response;（2） Wavelet packet decomposition technique can effectively filter out noise in aliasing wave;（3） Non-collinear beams mixing method has the capabilities to detect the internal uniformity of material.