Impact damage, caused by low-energy impact, is inevitable during the whole life time of carbon fiber reinforced plastic (CFRP) material. However, the barely visible impact damage (BVID) is difficult to be detected by visual methods. Ultrasonic thermography (UT) is an emerging nondestructive testing technique that visualizes damage in thermal images captured by an infrared (IR) camera when the material is stimulated by ultrasound. However, noise and blurry edges around the high-temperature areas may cause confusion and lead to unreliable results in the thermal images of UT test. In this paper, an impact damage inspection method is proposed based on manifold learning for the CFRP material. Low-power ultrasonic excitation is used for this UT. The IR image sequences are processed as datasets in high-dimensional space. These datasets are reduced to lower dimensions by manifold learning to find the intrinsic structure in the two-dimensional manifold. Each dimension of the embedding manifold correlates highly with one degree of freedom underlying the original pixel: steady and random components. The steady component, which reflects the temperature rise caused by damage, is used for VID and BVID detection. The experimental system was set up, and CFRP plate specimens with different impact damage were tested. All the impact damage could be detected and shown in reconstructed static image with little noise. The proposed method using image sequences could provide a visualized, reliable, and effective impact damage inspection and localization means for CFRP material during manufacturing and in service.

中文翻译：

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基于超声诱导热成像流形学习的 CFRP 冲击损伤检测


在碳纤维增强塑料（CFRP）材料的整个生命周期中，由低能量冲击引起的冲击损坏是不可避免的。然而，几乎不可见的冲击损伤（BVID）很难通过视觉方法检测到。超声波热成像 (UT) 是一种新兴的无损检测技术，当材料受到超声波刺激时，可通过红外 (IR) 相机捕获的热图像显示损坏情况。然而，高温区域周围的噪声和模糊边缘可能会造成混乱，导致 UT 测试的热图像结果不可靠。本文提出了一种基于流形学习的CFRP材料冲击损伤检测方法。该 UT 使用低功率超声波激励。红外图像序列被处理为高维空间中的数据集。通过流形学习将这些数据集降低到较低维度，以找到二维流形中的内在结构。嵌入流形的每个维度都与原始像素下的一个自由度高度相关：稳定和随机分量。稳定元件反映了损坏引起的温升，用于VID和BVID检测。搭建实验系统，对不同冲击损伤的CFRP板试件进行测试。所有的冲击损伤都可以被检测到并在重建的静态图像中显示，噪声很少。所提出的使用图像序列的方法可以为CFRP材料在制造和使用过程中提供可视化、可靠且有效的冲击损伤检测和定位手段。