激光诱导热波差分法分层检测金属次表面缺陷

Laminating Detection of Defects Under Metal Subsurface Using Difference Method of the Thermal Wave Induced by the Pump Laser

用固体材料吸收一维热传导模型求解一维热传导方程,获得了试样表面温度与试样缺陷深度、泵浦光调制频率的关系,进而推论出:控制调制频率确定热扩散长度就确定了可探测的埋在固体内部缺陷的深度范围。利用热波辐射产生试样表面温度变化引起邻近表面空气折射率变化的原理和垂直光热光偏转探测技术,建立了以全半导体激光为泵浦光和探测光的光热偏转检测装置,对Al块表面二维扫描检测到的热波信号作编码成像处理得到热波像。通过2个调制频率下热波像的差分处理获得了埋在次表面深度330μm处、厚度为50μm的沟槽缺陷,论证了热波差分成像检测方法对金属次表面缺陷实现分层成像检测的可行性。

One-dimension thermal conductivity equation is solved and the relationship between the surface temperature and the depth of defects and the modulating frequency of the pump laser is deduced. A detection setup based on the transversal photo-thermal deflection detection technique is established. The structure of the setup is smaller. In the setup two LD supply the pump beam and the probe beam respectively. Thermal wave images reconstructed by the detected signals are obtained by using two-dimension scanning on the surface of the metal sample Al. And a channel defect with thickness of 50 μm buried at the depth of 330 μm in the sample Al was detected by the method of amplitude difference of thermal waves signals under two modulating frequencies of the pump laser. It is shown that laminating detection of defects buried in metal Al is feasible by difference method of thermal wave images.