传统的激光超声无损检测技术已能够实现对宽度为亚毫米量级裂纹的非接触式无损检测,但其对更小的裂纹并不敏感。而非线性激光超声检测技术可实现对微裂纹的无损检测。其中,基于热调制的光声非线性混频技术一直广受学者关注。通过搭建光声非线性混频试验平台,研究光声非线性信号特征与激发源和泵浦源功率之间的关系,讨论了基础温度对非线性现象的影响,研究了基础位移对裂纹非线性机制转变的影响,可为进一步研究光声非线性混频中微裂纹的接触机制提供参考,也为利用光声非线性方法半定量、定量表征裂纹提供了理论依据。

The traditional laser ultrasonic non-destructive testing technology has been able to achieve non-contact nondestructive testing of cracks with a width of submillimeter, but it is not sensitive to smaller cracks. However, the nonlinear laser ultrasonic testing technology can realize the nondestructive testing of microcracks. Among them, the nonlinear optoacoustic frequency-mixing technology based on thermal modulation has been widely concerned by scholars. In this paper, an optoacoustic nonlinear frequency-mixing experiment platform was built. On the one hand, the relationship between the characteristics of the nonlinear optoacoustic signal and the power of the excitation source and the pump source was studied. On the other hand, the nonlinear phenomenon affected by base temperature was discussed. Besides, the influences of the base displacement generated by the base temperature on the transformation of the nonlinear mechanism in micro cracks was studied, which will be considered to provide a reference for further research on the contact mechanism of microcracks in nonlinear optoacoustic frequency-mixing technology, and also provide a theoretical basis for the semi-quantitative and quantitative characterization of cracks by using nonlinear optoacoustic methods.