Micro-fracture behaviors of needled short-chopped fiber reinforced phenolic aerogel composites based on in-situ X-ray micro-CT

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.