Research on the Detection of Silica/Phenolic Composite Surface Cracks Using Instantaneous High-Power Xenon Lamp-Induced Chirp-Pulsed Radar Thermography

In this present study, the high-power instantaneous xenon lamp-induced chirp-pulsed radar thermography was introduced to detect the surface crack of the silicon/phenolic composite which was widely used in the engine nozzle insulation sleeve. Two crack defect specimens were artificially made and detected by chirp-pulsed radar thermography to verify the detection ability of this approach. The cracks of two specimens were made by the diamond scribing process and laser ablation respectively. The differences between them were analyzed by the crack defect detection experiment. The crack defect made by the diamond scratching method is more consistent with the real situation according to the experimental results. The chirp-pulsed radar signal was extracted by the time/frequency signal extraction algorithms [cross-correlation (CC) and dual-orthogonal demodulation algo-rithms (DOD)]. The influence of parameters such as the power of xenon lamps, excitation frequency, reference pulse width or pulse time, and reference signal delay time on the detection results is mainly investigated by quantitative detection experiments. The results demonstrated that the CC peak and DOD amplitude are more sensitive than the phase when detected the surface crack of silica/phenolic composites. Meanwhile, the reflective phenomenon of the specimen's surface has a great impact on the detection results. The larger the excitation parameters (such as the excitation frequency and the signal pulse width), the larger the contrast of the crack defect and the smaller the signal-to-noise ratio (SNR). The delay time of the reference signal has a small impact on the SNR and contrast of crack detection. In summary, instantaneous high-power xenon lamp-induced chirp -pulsed radar thermography can realize the reliable quantitative detection of surface cracks of silicon/phenolic composite.