ABSTRACT

Among the Non-Destructive Testing (NDT) techniques available today, Active Infrared Thermal Testing (AIRTT) is certainly one of the most flexible and promising. The goal of this work was to compare the results obtained with a common Lock-in Thermal Test (LTT) and the same test using a true sinusoidal stimulation obtained through a closed-loop controller. The results showed a poor dynamic response of the common system and a lack of proportionality between the reference signal and the generated optical stimulation. To improve its response, it was implemented a PID controller using a light sensor to close the feedback loop. The amplitude images obtained with this controller showed a significant improvement in the results. Defects invisible with the common LTT were now identifiable. The phase images obtained using the controller with feedback revealed higher sensitivity with lower noise. Despite only one system was tested, the results show that the optical stimulation used in LTT is not very accurate and can/should be improved and, that a sensitivity 2.5 times higher than the common LTT was achieved with a real sinusoidal stimulation.

Abbreviation: NDT: Non-Destructive Tests; AIRTT: Active Infrared Thermal Testing; LTT: Lock-in Thermal Test; cLTT: common LTT; PID: Proportional, Integral and Derivative; CFRP: Carbon Fibre Reinforced Polymers; TTT: Transient Thermal Tests; LDR: light-dependent resistor; PMMA: Poly(methyl methacrylate)

摘要

在当今可用的无损检测 (NDT) 技术中，主动红外热测试 (AIRTT) 无疑是最灵活和最有前途的技术之一。这项工作的目的是比较使用普通锁定热测试 (LTT) 获得的结果和使用通过闭环控制器获得的真正正弦刺激的相同测试。结果表明，公共系统的动态响应较差，并且参考信号与产生的光刺激之间缺乏比例。为了改善其响应，它使用光传感器实现了一个 PID 控制器来关闭反馈回路。使用该控制器获得的幅度图像显示结果显着改善。现在可以识别普通 LTT 看不到的缺陷。使用带有反馈的控制器获得的相位图像显示出更高的灵敏度和更低的噪声。尽管只测试了一个系统，但结果表明 LTT 中使用的光学刺激不是很准确，可以/应该改进，并且使用真正的正弦刺激可以实现比普通 LTT 高 2.5 倍的灵敏度。

缩写： NDT：无损检测；AIRTT：主动红外热测试；LTT：锁定热测试；cLTT：普通LTT；PID：比例、积分和微分；CFRP：碳纤维增强聚合物；TTT：瞬态热测试；LDR：光敏电阻；PMMA：聚（甲基丙烯酸甲酯）