Tensile fatigue behavior and damage evolution of z-pinned carbon/phenolic woven composite using in-situ monitoring technology

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.