Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semi-transparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions.

中文翻译：

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使用脉冲红外热成像检测半透明玻璃纤维复合材料中的分层

由于其良好的强度/质量比，玻璃纤维增​​强塑料 (GFRP) 复合材料是一种广泛用于航空、电力生产、汽车和其他行业的常见材料。反过来，主动红外 (IR) 无损检测 (NDT) 是一种常见的检测技术，用于检测和表征 GFRP 中的结构缺陷。要测试的材料通常会受到光加热，这应该发生在材料表面。然而，GFRP 复合材料对于可见光和红外光谱带的光辐射都是半透明的。相应地，检测过程代表了光学和热现象的某种组合。因此，基于纯热扩散的已知表征算法不能应用于半透明材料。在这项研究中，GFRP 半透明现象已通过数值和实验研究应用于热无损检测。氙气闪光灯管和激光都已用于不透明和半透明测试对象的热刺激。已经表明，光热辐射穿透复合材料会降低较浅缺陷的可检测性，并且可以通过应用热成像信号重建 (TSR) 技术来提高信噪比。在检查半透明 GFRP 复合材料时，最有效的是激光加热，然后是 TSR 数据处理。讨论了利用激光加热对半透明材料进行缺陷表征的前景。神经网络已被用作评估复合材料缺陷深度的候选工具，