Development of microscopic thermography for small defects

研制了一种适用于复合材料和层合材料内部微小缺陷和损伤检测的热像无损检测系统。当样品加热和冷却时，拍摄并分析测试样品表面的红外热图像。传统的扫描型热成像仪被用来获得热图像与一些可选的放大透镜，包括显微镜透镜。通过实验和数值模拟，使用人工分层样品的缺陷尺寸的分辨率进行了研究。结果发现，样品的热导率起着重要的作用的分辨率。使用有效的冷却是提高分辨率的关键。在空冷条件下，GFRP和CFRP试件表面下的最小分层裂纹尺寸约为4 mm。对于厚度非常薄（厚度为60微米）的铜-聚酰亚胺层压柔性膜，能够检测到直径为1 mm的较小缺陷。本文提出了一种新的、更有效的冷却技术，即在被加热的试样上放置一个透红外固体板。在该方法中，当透明板与样品接触时，通过透明板获得样品表面的热图像。GFRP和CFRP样本均成功进行了缺陷检查。

A thermographic non-destructive inspection system, which is applicable for the examination of the small defects and damage embedded in composite and laminated materials, has been developed. The infrared thermal image of the surface of test samples is taken and analysed, when the samples are heated and cooled. A conventional scanning-type thermal imager was used to obtain the thermal image with some optional magnification lens including microscope lens. The resolution in defect size was examined both experimentally and numerically by using artificial delaminated samples. It was found that the thermal conductivity of the sample plays an important role for the resolution. The use of an efficient cooling is a key for the improvement of the resolution. A minimum delaminated flaw size in the sub-surface of GFRP and CFRP samples was around 4mm in diameter under air cooling. A smaller flaw as large as 1mm in diameter was able to detect for a copper-polyimide laminated flexible film whose thickness is exceptionaly thin (60 microns in thickness). A new and more effective cooling technique, in which an infrared transparent solid plate is in contact on the heated test sample, has been developed. The thermal image of the sample surface is obtained through the transparent plate as soon as the plate is in contact on the sample in this method. The successful flaw inspection was demonstrated both in GFRP and CFRP samples.