Needled short-chopped fiber reinforced phenolic aerogel composites (PAC) are the most promising thermal protection materials for space applications. However, the complex microstructures deriving from the irregular needling yarns severely limits the revealing of their fracture mechanisms. Herein, for the first time, the micro-fracture behaviors of PAC are innovatively revealed using in-situ X-ray micro-CT under tensile loading. Furthermore, the high-precision finite element analysis of stress evolution is realized by establishing PAC model based on the micro-CT slices. The results indicate that the needling yarns will result in the enrichment of resin aerogel, leading to the stress concentration and micro-cracks initiation during loading. And the needling yarns can effectively hinder the separation and orientation of short-chopped fibers and retard the stress transmission between fibers and matrix, which are the main strengthening mechanisms of PAC. The present results will give references for revealing the fracture mechanisms of composites enhanced by needled fibers.

针刺短切纤维增强酚醛气凝胶复合材料（PAC）是最有前途的空间应用热防护材料。然而，源自不规则针刺纱线的复杂微观结构严重限制了其断裂机制的揭示。在此，首次使用原位 X 射线 micro-CT 在拉伸载荷下创新地揭示了 PAC 的微断裂行为。此外，高精度有限通过建立基于显微CT切片的PAC模型，实现应力演化的元分析。结果表明，针刺纱线会导致树脂气凝胶富集，导致加载过程中应力集中和微裂纹萌生。而针刺纱能有效地阻碍短切纤维的分离和取向，延缓纤维与基体之间的应力传递，是PAC的主要强化机制。本研究结果将为揭示针刺纤维增强复合材料的断裂机制提供参考。