Infrared Imaging for Quantitative Defect Detection in Composite Structures

由于其优越的机械性能、重量轻和耐腐蚀，复合材料被用于民用和军事部门的各种结构部件中。现代飞机（如波音787和空客A380）、船舶、汽车、风力涡轮机、体育用品和许多其他高性能结构中都可以找到由复合材料制成的部件。不幸的是，这些材料的缺陷，无论是制造还是操作条件，都会大大降低结构的最终性能，甚至在灾难性故障的情况下影响人类的安全。为了保证结构性能和安全，工程师需要知道缺陷的存在、大小和位置（就像肿瘤学家医生需要知道病人肿瘤的范围以最好地治愈它一样）。红外热成像技术为复合材料结构的缺陷检测提供了独特的优势，包括广泛的覆盖范围、检测速度和易于解释的诊断图像。该项目将通过改进复合材料中缺陷的尺寸和位置的确定来推进红外热成像技术的发展。这种能力将允许维护工程师和结构所有者在检测到损坏事件后做出明智的补救措施决定，最终提高结构的可靠性和安全性。该项目的研究目标是通过定量检测复合材料结构的缺陷来推进已知的红外热成像技术的无损检测（NDT）。目前的热成像能力允许定性缺陷检测，定量预测仅基于简单和不切实际的1-D热扩散模型。本研究将基于“虚拟热源”（VHS）的新概念，开发真实的复合材料三维热扩散模型，以模拟主动加热后结构内部缺陷产生的多余表面热量。三维热扩散问题的格林函数解也将寻求解释最一般的缺陷情况（例如非平面缺陷）。该模型将预测测试对象中的温度场，作为可量化缺陷特征的函数，包括(1)缺陷深度，(2)缺陷尺寸，(3)缺陷方向。理论模型将通过一系列实验热成像测试进行验证和迭代，这些测试将在UCSD现有的样品上进行，包括一个独特的9米长复合风力涡轮机叶片（CX-100叶片），其中包含45个充分记录的缺陷，以及几个具有代表性的复合材料飞机结构面板。

Due to their superior mechanical performance, light-weight and resistance to corrosion, composite materials are used in a variety of structural components in the civil and military sectors. Parts made of composite materials are found in modern aircraft (e.g., Boeing 787 and Airbus A380), ships, cars, wind turbines, sporting goods and many other high performance structures. Unfortunately, defects in these materials, caused by either manufacturing or operational conditions, can greatly reduce the ultimate performance of the structure, and even impact human safety in the case of catastrophic failures. In order to guarantee structural performance and safety, engineers need to know the presence, size and position of the flaws (in much the same manner that an oncologist doctor needs to know the extent of a tumor in a patient to best cure it). The technique of Infrared Thermography offers unique advantages for defect detection in composite structures, including broad coverage, speed of inspection and easily-interpretable diagnostic images. This project will advance the state-of-the-art in Infrared Thermography by improving the determination of the size and the position of a flaw in the composite material. This capability will allow maintenance engineers and structures' owners to make informed decisions on remedial steps following a damage detection event, ultimately increasing the reliability and the safety of the structure.The research goal of this project is to advance the known technique of Infrared Thermography for the Non-Destructive Testing (NDT) of composite structures by enabling quantitative defect detection. Current Thermographic capabilities allow for qualitative defect detection, with quantitative predictions only based on simplistic and unrealistic 1-D heat diffusion models. This research will develop realistic 3-D heat diffusion models for composite materials based on a novel concept of "Virtual Heat Source" (VHS) to simulate the excess surface heat produced by an internal defect in the structure following active heating. A Green's function solution to the 3-D heat diffusion problem will be also sought to account for the most general defect cases (e.g. non-planar defects). The models will predict the temperature field in the test object as a function of quantifiable defect features, including (1) defect depth, (2) defect size, and (3) defect orientation. The theoretical models will be validated and iterated by a series of experimental thermographic tests conducted on existing specimens at UCSD, including a unique, 9-m long composite wind turbine blade (CX-100 blade) containing 45 well-documented defects, and several panels representative of composite aircraft construction.