High temperature structure-property evolution of orthogonal three-directional carbon fiber/nanoporous phenolic composite

Revealing the high temperature multi-scale structure and mechanical-thermal performance evolution of ablative thermal protection materials is of great scientific significance to further improve the high temperature service performance. In this paper, the orthogonal three-dimensional carbon fiber/nanoporous phenolic composite with lightweight-insulation-bearing integration is taken as an example, and the multi-scale structural evolution of the porous structure, fiber/matrix interface and braided structure of the composite under high temperature environment (400-1200 ℃) is studied. Change rules of mechanical, thermal insulation and ablation properties caused by structural evolution are explored. The results show that the composite can maintain the nanoporous structure after high temperature treatment in the range of 400-1200 ℃. Besides, due to the dimensional effect of the orthogonal three-dimensional preform, the composite has no obvious volume shrinkage and excellent high temperature structural stability. However, the carbonization shrinkage of phenolic resin at high temperature will lead to delamination between matrix yarns and cracking in yarns, which lead to the gradual attenuation of mechanical properties of composites. At the same time, the carbonization of phenolic resin will also lead to a significant increase in the thermal conductivity of the matrix, which will lead to the deterioration of the thermal insulation performance. In addition, due to the good high-temperature dimensional ability of the orthogonal three-dimensional fiber preform, the linear ablation rate of the composites after high-temperature treatment at 2000 ℃ and 4.18 MW/m² is less different from that of the original composite. The results of this paper can provide an important theoretical reference for the selection and performance improvement of ablative thermal protection materials.