Carbon/phenolic composite, as structural materials for aerospace, undergoes static and dynamic loading which can affect the structural integrity of components. This paper aims to comprehensively investigate the mechanical properties and damage evolution mechanisms of z-pinned carbon/phenolic woven composite subjected to static tensile and different levels of tension-tension fatigue loading. The essential correlation between damage modes and acoustic emission (AE) signals of carbon/phenolic composite was first established. The AE signals were processed using the Hilbert-Huang transform method to obtain the percentage of damage modes at various load levels. The results showed that the peak frequency ranges of the three damage modes, matrix cracking, debonding, and fiber breakage, were 100–200 kHz, 200–300 kHz, and over 300 kHz, respectively. Moreover, the damage evolution mechanisms can be revealed using the OM-AE monitoring method. It was found that the dominant damage modes were all matrix cracking. The fatigue damage occurs at the edge of the specimen, and the three damage modes interact with each other on a microscopic scale. Cracks expand from the edge to the center at low stress. The developed OM-AE online damage monitoring system allows real-time damage monitoring and accurate recognition of damage modes.

中文翻译：

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使用原位监测技术研究 z 型钉扎碳/酚醛编织复合材料的拉伸疲劳行为和损伤演化

碳/酚醛复合材料作为航空航天结构材料，承受静态和动态载荷，这会影响部件的结构完整性。本文旨在全面研究z钉扎碳/酚醛编织复合材料在静态拉伸和不同水平的拉-拉疲劳载荷作用下的力学性能和损伤演化机制。首次建立了碳/酚醛复合材料损伤模式与声发射（AE）信号之间的本质相关性。使用 Hilbert-Huang 变换方法处理 AE 信号，以获得不同负载水平下损坏模式的百分比。结果表明，基体破裂、脱粘和纤维断裂三种损伤模式的峰值频率范围分别为100-200 kHz、200-300 kHz和超过300 kHz。此外，使用 OM-AE 监测方法可以揭示损伤演化机制。结果发现，主要的损伤模式都是基体开裂。疲劳损伤发生在试件边缘，三种损伤模式在微观尺度上相互作用。在低应力下裂纹从边缘向中心扩展。开发的OM-AE在线损伤监测系统可以实时监测损伤并准确识别损伤模式。