MS&P: Optical Fiber Sensors for In-Situ Temperature and Strain Measurements in Composite

将开发用于高温（1000℃）复合材料加工的光纤传感器。具体来说，新型光纤将用于两种类型的原位测量：温度和染色。温度传感器将由稀土掺杂剂合成，这将允许在500- 1200℃范围内进行空间分辨温度测量。本文将研究基于法布里-珀罗光栅的应变传感器和使用光学时域反射法的应变传感器。所开发的温度和应变传感器将被整合到通过化学蒸汽渗透（CVI）生产的纤维增强、陶瓷和金属间基复合材料中。因为这些材料已经包含了光纤，所以加入额外的光纤传感器不会显著扰乱其微观结构。目前正在开发各种先进的热梯度CVI工艺，作为该项目的一部分，将开发的光纤传感器将使监测加工过程中的温度梯度成为可能。一个相对简单的热梯度CVI系统将用于在复合材料制造过程中进行光纤的原位温度测量。这些材料的微观结构也将被定量表征，并建立了渗透过程的数值模型来分析温度梯度和微观结构演变。模型计算和实验测量之间的比较将提供对渗透过程的深入了解，并展示使用光纤温度传感器的潜力。应变传感器将在加工过程中提供测量，更重要的是，它们将使测量复合材料使用时的应变成为可能。这些原位应变测量为研究材料的应力-应变行为提供了一种新的方法。在脆性基复合材料中，基体相通常在材料失效之前很久就开始微裂纹，因此，这些原位应变测量特别重要，因为它将有可能在宏观破坏实际发生之前监测这些材料的退化。

Optical fiber sensors will be developed for applications in composite materials that are processed at high-temperatures (1000oC). Specifically, novel optical fibers will be used for two types of in-situ measurements: temperature and stain. Temperature sensors will be synthesized with rare-earth dopants that will permit spatially resolved temperature measurements in the range of 500- 1200oC. Strain sensors based on Fabry-Perot gratings and using optical time domain reflectometry will both be investigated. The temperature and strain sensors that are developed will be incorporated in fiber-reinforced, ceramic and intermetallic matrix composites that will be produced by chemical vapor infiltration (CVI). Because these materials already contain fibers, the incorporation of additional optical fiber sensors will not significantly perturb the microstructure. A variety of advanced, thermal gradient CVI processes are currently being developed, and the optical fiber sensors that will be developed as part of this program will make it possible to monitor temperature gradients during processing. A relatively simple thermal gradient CVI system will be used to make in- situ optical fiber temperature measurements during composite fabrication. The microstructure of these materials will also be characterized quantitatively, and a numerical model of the infiltration process will be developed to analyze both the temperature gradients and the microstructure evolution. Comparisons between the modeling calculations and the experimental measurements will provide insight into the infiltration process, and demonstrate the potential for using optical fiber temperature sensors. The strain sensors will provide measurements during processing, and more importantly, they will make it possible to measure strain when the composite is in use. These in-situ strain measurements offer a novel method to study the stress-strain behavior of the material. In brittle matrix composites, the matrix phase typically begins to microcrack long before the material fails, thus these in-situ strain measurements are particularly important because it will be possible to monitor the degradation of these materials before macroscopic failure actually occurs.