A real-time, in-process cure monitoring system employing a guided wave-based concept for carbon fiber reinforced polymer composites was developed. The system included a single piezoelectric disc that was bonded to the surface of the composite for excitation, and an embedded phase-shifted fiber Bragg grating for sensing. The phase-shifted fiber Bragg grating almost simultaneously measured both quasi-static strain and the ultrasonic guided wave-based signals throughout the cure cycle. A traditional FBG was also used as a base for evaluating the high sensitivity of the phase-shifted fiber Bragg grating sensor. Composite physical properties (degree of cure and glass transition temperature) were correlated to the amplitude and time of arrival of the guided wave-based measurements during the cure cycle. In addition, key state transitions (gelation and vitrification) were identified from the experimental data. The physical properties and state transitions were validated using cure process modeling software (e.g. RAVEN®). This system demonstrated the capability of using an embedded phase-shifted fiber Bragg grating to sense a wide bandwidth of signals during cure. The distinct advantages of a fiber optic-based system include multiplexing of multiple gratings along a single optical fiber, small size compared to piezoelectric sensors, ability to embed or surface mount, utilization in harsh environments, electrically passive operation, and electromagnetic interference (EMI) immunity. The embedded phase-shifted fiber Bragg grating fiber optic sensor can monitor the entire life-cycle of the composite structure from curing, post-cure/assembly, and in-service creating “smart structures”.

中文翻译：

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基于导波的系统，使用压电盘和相移光纤布拉格光栅实时监测复合材料的固化

开发了一种针对碳纤维增强聚合物复合材料采用基于导波概念的实时过程中固化监控系统。该系统包括一个粘合到复合材料表面用于激励的单个压电盘，以及一个用于传感的嵌入式相移光纤布拉格光栅。在整个固化周期中，相移光纤布拉格光栅几乎同时测量准静态应变和基于超声导波的信号。传统的光纤光栅也被用作评估相移光纤布拉格光栅传感器高灵敏度的基础。复合材料的物理特性（固化程度和玻璃化转变温度）与固化周期期间基于导波的测量的幅度和到达时间相关。此外，还从实验数据中确定了关键的状态转变（凝胶化和玻璃化）。使用固化过程建模软件（例如RAVEN®）验证物理特性和状态转变。该系统展示了使用嵌入式相移光纤布拉格光栅在固化过程中感测宽带宽信号的能力。基于光纤的系统的独特优势包括沿单根光纤复用多个光栅、与压电传感器相比尺寸小、能够嵌入或表面安装、在恶劣环境中使用、电无源操作和电磁干扰 (EMI)免疫。嵌入式相移光纤布拉格光栅光纤传感器可以监控复合材料结构的整个生命周期，从固化、后固化/组装到在役创建“智能结构”。