Abstract Fiber fracture is a major contributor for the initiation of failure in fiber-reinforced polymer composites. The purpose of this study was to identify where damage occurs when a fiber fractures in a composite. Because this dynamic event occurs in less than 100 1ns, obtaining experimental evidence has been prohibitively difficult. Here, we report a novel method using a model composite, comprised of a spirolactam-based mechanophore-functionalized epoxy resin with a single embedded glass fiber. The ductile epoxy matrix is loaded under tension, which transfers load through interfacial shearing to the embedded brittle fiber, causing the fiber to break into segments. Fluorescence lifetime imaging microscopy (FLIM) is used to visualize regions of mechanophore activation and quantify changes in the dye's local environment such as relaxations on the nanosecond timescale. FLIM of these single fiber fragmentation test (SFFT) samples reveals localized damage zones in the epoxy matrix, not only at the point of fiber fragmentation, but also at distances remote from the fracture site that extend radially into the matrix up to two fiber diameters. The average mechanophore lifetime in the bulk epoxy is (1.5 ± 0.5) ns and in the damage regions is (0.75 ± 0.15) ns. This new data reveals the existence of polymer matrix yielding, which occurs during the fiber fracture event, and agrees with a dynamic model that predicts yielding behavior in the matrix during fracture. These results suggest that the damage from fiber fracture is more extensive than previously recognized. This new approach can be used to elucidate damage in other mechanical tests. The subsequent insights into composite damage mechanisms promises to dramatically accelerate the development of tough, durable, and damage tolerant composites.

中文翻译：

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在单纤维复合材料中使用机械团交联环氧树脂进行损伤传感

摘要 纤维断裂是导致纤维增强聚合物复合材料失效的主要因素。本研究的目的是确定复合材料中纤维断裂时发生损坏的位置。由于这一动态事件发生的时间不到 100 1ns，因此获得实验证据非常困难。在这里，我们报告了一种使用模型复合材料的新方法，该模型复合材料由基于螺内酰胺的机械团官能化环氧树脂和单个嵌入玻璃纤维组成。韧性环氧树脂基体在张力下加载，通过界面剪切将载荷传递给嵌入的脆性纤维，导致纤维断裂成片段。荧光寿命成像显微镜 (FLIM) 用于可视化机械团激活区域并量化染料的变化' s 局部环境，例如纳秒时间尺度上的松弛。这些单纤维碎裂测试 (SFFT) 样品的 FLIM 揭示了环氧树脂基质中的局部损伤区域，不仅在纤维碎裂点，而且在远离断裂部位的距离处，径向延伸到基体中达两个纤维直径。本体环氧树脂中的平均机械寿命为 (1.5 ± 0.5) ns，损坏区域为 (0.75 ± 0.15) ns。这一新数据揭示了聚合物基体屈服的存在，它发生在纤维断裂事件期间，并与预测断裂过程中基体屈服行为的动态模型一致。这些结果表明，纤维断裂造成的损害比以前认识到的更为广泛。这种新方法可用于阐明其他机械测试中的损坏。