本文關(guān)鍵詞：真實(shí)微裂紋的激光超聲非線性混頻檢測研究　出處：《南京理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 激光超聲 無損檢測 非線性混頻效應(yīng) 真實(shí)裂紋

【摘要】：采用全光學(xué)方法檢測聲波與開合裂紋相互作用后在頻域內(nèi)的非線性混頻效應(yīng),達(dá)到檢測裂紋位置的目的。一束連續(xù)激光被分束后分別經(jīng)過兩個(gè)聲光調(diào)制器,成為幅度調(diào)制的高頻(f_H)激發(fā)光和低頻(f_L)加熱光。當(dāng)?shù)皖l加熱光輻照于裂紋之上時(shí)會(huì)引起裂紋"呼吸"(周期性開合)。此時(shí)激發(fā)光激發(fā)出頻率為f_H的聲波與開合裂紋相互作用后產(chǎn)生非線性混頻信號(hào)(f_H±f_L),最后由測振儀或光偏轉(zhuǎn)裝置接收光信號(hào)并送至鎖相放大器。實(shí)驗(yàn)中輻照在樣品上的激發(fā)光、加熱光和檢測光的光斑始終重合。移動(dòng)樣品在裂紋附近掃查,通過觀察非線性混頻信號(hào)的幅值變化可以得到裂紋的位置信息,混頻信號(hào)出現(xiàn)表示三束光到達(dá)裂紋區(qū)域。隨著三束光源逐步靠近裂紋中心,混頻信號(hào)幅值逐漸增大。當(dāng)增大到最大值后(三束光源達(dá)到裂紋中心區(qū)域)混頻信號(hào)幅值開始逐漸減小(三束光源逐漸遠(yuǎn)離裂紋區(qū)域)最終趨于平緩,此時(shí)混頻信號(hào)消失。所以可以通過觀察混頻信號(hào)的幅值變化來得到裂紋的位置信息。由光偏轉(zhuǎn)裝置來接收聲信號(hào)的實(shí)驗(yàn)中,進(jìn)行擴(kuò)束改進(jìn)之后的光偏轉(zhuǎn)裝置觀測到了非線性混頻信號(hào),這表明全光學(xué)的檢測方法可以用來對(duì)非線性混頻信號(hào)的實(shí)驗(yàn)研究,且由于全光學(xué)檢測方法具有非接觸、可聚焦到很小固可以對(duì)復(fù)雜樣品檢測等優(yōu)點(diǎn),采用全光學(xué)檢測方法具有更多實(shí)用價(jià)值。利用非線性光聲混頻效應(yīng)來檢測裂紋的方法對(duì)實(shí)際的閉合裂紋的檢測靈敏度遠(yuǎn)高于傳統(tǒng)的線性激光超聲裂紋檢測方法,可為裂紋的光聲無損檢測提供新的解決思路和技術(shù)。
[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 鹵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.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB302.5

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本文編號(hào)：1419457