Abstract In this work, carbon fiber needle-punching preforms were designed into two structure according to the density change along the thickness direction. One structure is designed to two layers with low-density layer and high-density layer, and the other is to three layers with low-density exterior layer and high-density interior layer. Then the effect of the preform with different structure on the densification rate and compressive properties of C/C composites was investigated. The results show that both two designed preforms can effectively avoid surface blocking, and lead to the faster densification rate of C/C composites during the chemical vapor infiltration processes. These results are attributable to the change of pore size distribution and pyrocarbon thickness, which was caused by fiber architecture designs. Meanwhile, these structural changes can improve the compressive strength of C/C composites, especially for the three-layer preforms. When the density of preforms is 0.45 g/cm3, C/C composites with three-layer preform has the highest compressive strength. The damage of most C/C composites with two and three-layer preforms is caused by shear or delamination failure, while that of C/C composites with common preforms usually caused by matrix collapse. Cracks in C/C composites with two and three-layer preforms always happened on the low-density layer, and consequently ceased or changed propagation direction in the interface between two layers.

中文翻译：

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层状设计预制件的碳/碳复合材料的致密化率和力学性能

摘要 本工作根据碳纤维针刺预制件沿厚度方向的密度变化，将其设计成两种结构。一种结构设计为低密度层和高密度层两层，另一种结构设计为三层低密度外层和高密度内层。然后研究了不同结构的预制件对C/C复合材料致密化率和压缩性能的影响。结果表明，两种设计的预制件均能有效避免表面堵塞，并在化学气相渗透过程中使 C/C 复合材料的致密化速度更快。这些结果归因于孔径分布和焦炭厚度的变化，这是由纤维结构设计引起的。同时，这些结构变化可以提高 C/C 复合材料的抗压强度，特别是对于三层预制件。当预制件的密度为0.45 g/cm3时，三层预制件的C/C复合材料的抗压强度最高。大多数两层和三层预制件的C/C复合材料的损坏是由剪切或分层破坏引起的，而普通预制件的C/C复合材料的损坏通常是由基体坍塌引起的。两层和三层预制件的 C/C 复合材料的裂纹总是发生在低密度层上，从而停止或改变两层之间界面的传播方向。具有三层预制件的 C/C 复合材料具有最高的抗压强度。大多数两层和三层预制件的C/C复合材料的损坏是由剪切或分层破坏引起的，而普通预制件的C/C复合材料的损坏通常是由基体坍塌引起的。两层和三层预制件的 C/C 复合材料的裂纹总是发生在低密度层上，从而停止或改变两层之间界面的传播方向。具有三层预制件的 C/C 复合材料具有最高的抗压强度。大多数两层和三层预制件的C/C复合材料的损坏是由剪切或分层破坏引起的，而普通预制件的C/C复合材料的损坏通常是由基体坍塌引起的。两层和三层预制件的 C/C 复合材料的裂纹总是发生在低密度层上，从而停止或改变两层之间界面的传播方向。