复合材料紧固孔分层激光超声量化表征试验

提出解决飞机复合材料结构紧固孔分层检测问题的途径。基于激光超声技术，进行复合材料紧固孔分层的量化表征试验。制备碳纤维增强复合材料紧固孔试样，根据复合材料中激光超声的激发参量选取原则，利用材料受脉冲激光辐照作用产生的热弹效应激发超声波，提取表征紧固孔区域分层缺陷的超声信号；分析影响缺陷表征准确度的关键因素，发现脉冲激光光斑尺寸（直径1~5 mm）变化对紧固孔分层的表征不产生显著影响；基于穿透法和脉冲反射法进行激光超声C扫描检测，得到紧固孔区域分层缺陷的形状、尺寸和位置特征。研究结果表明，利用激光超声技术的非接触式激发、接收和高分辨力特点，可以准确测得紧固孔区域分层缺陷导致的波反射和衰减，有效表征飞机复合材料结构的紧固孔分层缺陷。

Quantitative Characterization Test of Fastening Hole Delamination in Composites with Laser Ultrasonics

An effective method for the detection of fastening hole delamination in composite aeronautical structures is proposed. Tests for the quantitative characterization of drilling-induced delamination in composites are conducted based on the laser ultrasonic technique. A specimen of carbon fiber reinforced plastic material is prepared, and the fastening holes are processed. Ultrasonic waves are generated by the thermo elastic effect of the material as it is illuminated by a pulse laser whose parameters are selected according to the principle of laser ultrasonic generation in composites. Ultrasonic signals that could be used to characterize the subsurface drilling-induced delamination are extracted. Major factors that might influence the characterization precision of the delamination are analyzed, and it can be seen that the dimension of the laser spot size (1-5 mm) has little influence on the characterization of the delamination. Typical C-scan testing of the specimen with laser ultrasonic technique is accomplished based on the transmission and pulse echo method, and the features of morphology, dimension and position of the drilling-induced delamination are obtained. The results prove that based on the advantages of the laser ultrasonic technique (e.g. non-contact generation and detection, high resolution), the drilling-induced delamination in composite aeronautical structures can be characterized effectively by measuring the wave reflection and attenuation induced by the delamination.