真实微裂纹的激光超声非线性混频检测研究

发布时间：2018-01-13 15:28

本文关键词：真实微裂纹的激光超声非线性混频检测研究　出处：《南京理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：采用全光学方法检测声波与开合裂纹相互作用后在频域内的非线性混频效应,达到检测裂纹位置的目的。一束连续激光被分束后分别经过两个声光调制器,成为幅度调制的高频(f_H)激发光和低频(f_L)加热光。当低频加热光辐照于裂纹之上时会引起裂纹"呼吸"(周期性开合)。此时激发光激发出频率为f_H的声波与开合裂纹相互作用后产生非线性混频信号(f_H±f_L),最后由测振仪或光偏转装置接收光信号并送至锁相放大器。实验中辐照在样品上的激发光、加热光和检测光的光斑始终重合。移动样品在裂纹附近扫查,通过观察非线性混频信号的幅值变化可以得到裂纹的位置信息,混频信号出现表示三束光到达裂纹区域。随着三束光源逐步靠近裂纹中心,混频信号幅值逐渐增大。当增大到最大值后(三束光源达到裂纹中心区域)混频信号幅值开始逐渐减小(三束光源逐渐远离裂纹区域)最终趋于平缓,此时混频信号消失。所以可以通过观察混频信号的幅值变化来得到裂纹的位置信息。由光偏转装置来接收声信号的实验中,进行扩束改进之后的光偏转装置观测到了非线性混频信号,这表明全光学的检测方法可以用来对非线性混频信号的实验研究,且由于全光学检测方法具有非接触、可聚焦到很小固可以对复杂样品检测等优点,采用全光学检测方法具有更多实用价值。利用非线性光声混频效应来检测裂纹的方法对实际的闭合裂纹的检测灵敏度远高于传统的线性激光超声裂纹检测方法,可为裂纹的光声无损检测提供新的解决思路和技术。
[Abstract]:An all-optical method is used to detect the nonlinear mixing effect of acoustic waves interacting with open cracks in frequency domain to detect the crack position. A continuous laser beam is divided into two acousto-optic modulators. The excitation light at high frequency and the heating light at low frequency by means of amplitude modulation. When the low frequency heating light is irradiated on the crack, it causes the crack "respiration" (periodic opening and closing). At this time, the excited light excites the interaction of the acoustic wave with the frequency fStuh and the opening and closing cracks to produce the nonlinear mixing signal (FH 卤FSP L). Finally, the optical signal is received by the vibrator or the optical deflection device and sent to the phase-locked amplifier. In the experiment, the excited light is irradiated on the sample, the spot of the heating light and the detecting light always coincide. The moving sample is scanned near the crack. By observing the amplitude change of the nonlinear mixing signal, the location information of the crack can be obtained. The mixing signal indicates that three beams of light arrive at the crack area, and with the three light sources gradually approaching the crack center. The amplitude of the mixing signal increases gradually. When the amplitude of the mixing signal increases to the maximum value (the three-beam light source reaches the crack center region) the amplitude of the mixing signal begins to decrease gradually (the three-beam light source is gradually away from the crack area) and finally tends to smooth. In this case, the mixing signal disappears, so the crack position information can be obtained by observing the amplitude change of the mixing signal. In the experiment, the optical deflection device is used to receive the sound signal. The nonlinear mixing signal is observed in the improved optical deflection device, which indicates that the all-optical detection method can be used for the experimental study of nonlinear mixing signal. And because the all-optical detection method has the advantages of non-contact, can focus to a very small solid can be used for the detection of complex samples and other advantages. Using all-optical detection method has more practical value. The detection sensitivity of nonlinear photoacoustic mixing method is much higher than that of traditional linear laser ultrasonic crack detection method. It can provide new solutions and techniques for photoacoustic nondestructive detection of cracks.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB302.5

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