Development of Thermographic NDTTechnique Based on Lock-in Measurement of Thermal Wave Response for Structural Integrity Assessment of Aging Aircraft

本项目开发了一种新的用于老化飞机结构完整性评估的定量无损检测技术。所得结果总结如下：1。为了检测裂纹，采用锁相热像仪测量了周期调制电流作用下裂纹尖端附近的奇异电热场。对该方法在钢、铝合金板中嵌入裂纹识别中的分辨率和适用性进行了实验研究。在锁模热像中，裂纹尖端处观察到明显的奇异电热场。准确地确定了裂纹的位置和尺寸，证明了该技术的可行性。针对材料损耗缺陷和分层缺陷，提出了一种基于周期性加热下表面温度锁定测量的热成像无损检测技术。实验研究了该方法在检测平板底孔缺陷和分层缺陷中的适用性。采用锁相热像仪采集同相和异相温度幅值图像，与周期加热的参考信号同步。在此基础上，提出了一种基于脉冲加热瞬态温度的热成像无损检测技术。利用傅立叶级数分析了反映缺陷尺寸、形状和深度等缺陷参数的温度下降曲线。发展的技术应用于航空结构材料损耗缺陷和分层缺陷的识别。结果表明，利用所开发的热成像无损检测技术可以准确地确定缺陷参数。提出了一种基于锁相红外热像仪相位延迟测量的混凝土结构分层缺陷定量无损检测技术。通过对比变化可以估计缺陷的位置和尺寸，通过相位延迟与加热周期的关系可以估计缺陷的深度。被动电位CT法是一种新的监测技术。采用逆分析方法对结构上的压电薄膜表面电位分布进行测量。少

The present project developed a new quantitative nondestructive testing (NDT) technique for structural integrity assessment of aging aircrafts. The results obtained are summarized as follows.1. For detecting cracks, singular electrothermal field near crack tips under the application of periodically modulated electric current was measured using lock-in thermography. Experimental investigations were made on the resolution and the applicability in the identification of cracks embedded in steel and aluminum alloy plates. Significant singular electrothermal field was observed at the crack tip in die lock-in thermal image. Location and size of the crack were accurately determined, demonstrating the feasibility of the proposed technique.2. For material loss defects and delamination defects, a thermographic NDT technique based on the lock-in measurement of the surface temperature under periodical heating was developed. Experimental study was made on the applicability to the detection of flat b … More ottom hole defects and delamination defects. In-phase and out-of-phase temperature amplitude images were taken by the lock-in thermography, synchronized to the reference signal of the periodical heating. Further, another thermographic NDT technique based on the transient temperature under the pulse heating was developed. Temperature descent curve which reflects defect parameters such as size, shape and depth of defects was analyzed using Fourier series. Developed techniques were applied to the identification of material loss defects and delamination defects in aerospace structures. It was found that defect parameters can be accurately determined by the developed thermographic NDT techniques.3. Quantitative NDT technique for delamination defects in concrete structures was developed based on the phase delay measurement using a lock-in infrared thermography. Location and size of the defect can be estimated from the contrast change and depth can be estimated from the relationship between phase delay and heating period.4. Passive electric potential CT method was developed as a new monitoring technique. Electric potential distribution measurement on the surface of piezoelectric film glued on the structure was processed by inverse analysis. Less