The Asf Mode Wedge Wave Laser Ultrasonic Experimental Research

Anti-symmetric flexural mode wedge waves have drawn great attention from researchers at home and abroad due to their attractive characteristics. When Anti-symmetric flexural mode wedge waves travels along the tip of a perfect wedge, their energy is tightly confined around the apex with the absence of dispersion, low phase velocity. In this dissertation, a novel differential optical beam deflection detection system is created and ASF mode wedge waves were successfully detected by using this detection system and their characteristics of dispersion and attenuation were discussed.With the summary of detection techniques on ASF mode wedge waves, a novel differential optical beam deflection detection system is introduced. Based on the features of differential optical detection technology, optical deflection plane is placed perpendicular to the propagation plane of ASF mode wedge waves. In this way, the spatial resolution of signals is improved. Moreover, the traditional triangular prism is replaced by double semi-circular beam splitter. Optical devices are then reduced as only one focusing lens with appropriate focusing length is used. This greatly reduces optical noise and improves signal noise ration.By using this differential optical beam deflection detection system, studies are made on ASF mode wedge waves from all aspects. For wedges with different angles, Time-Displacement waveforms are obtained; for the same sample, fix the exciting point and gradually move the detection point with the same steps along the tip of the wedge, surface image can be drawn. By the means of 2D FFT, dispersion graphs can be obtained; By moving the samples at the same steps to change the distance from the tip of the wedges while keeping the relative distance of exciting-detection point, Time-Displacement waveforms are obtained as well as the surface image at this direction. Through integral calculations, finally energy distributing graphs are obtained. Through the analysis of the results, we can find:with the increase of angle, the ASF modes will reduce; ASF mode wedge waves are dispersive along the tip of the aluminum samples used in this dissertation. Based on the Phase Velocity-Frequency graphs, each mode of the corresponding wedge is separated clearly; the energy of ASF mode wedge waves is tightly confined on the apex. Away from the tip of wedges, the energy of ASF mode wedge wave will attenuate exponentially. At the distance away from the tip about two wave length, the energy of ASF mode wedge waves will attenuate to a stable value.The results of this dissertation may provide references for the reserches on the characteristics of ASF mode wedge waves. It also provides the possibilities for the ASF mode wedge waves to be applied to non-destructive testing of wedge-like engineering components as well as the siganal process.