In order to predict the effective thermal conductivities of three-dimensional (3D) braided carbon/carbon (C/C) composites with randomly distributed void defects. Two-scale prediction model is developed based on the asymptotic homogenization method. Unit cell models both on fiber-scale and fiber bundle-scale are established according to the scanning electron microscopy observation of the material, and the randomly distributed void defects are considered. The effective thermal conductivities of fiber bundles with void defects are predicted firstly, then the effective thermal conductivities of the 3D braided C/C composites are predicted considering void defects in matrix pocket and interface by introducing the predicted thermal conductivities of fiber bundles. The predicted effective thermal conductivities agree well with the experimental results, demonstrating the validity of the two-scale prediction model. A parametric study is then conducted to analyze the effects of void volume fraction and interfacial thermal conductivity on the predictions of the developed model. The results show that the random distribution of void defects has a little effect on the effective thermal conductivities, while the void volume fraction has a significant effect on the effective thermal conductivities. The thermal conductivities decrease generally linearly with the increase of void volume fractions, and the effect of void volume fraction of matrix pocket is greater than that of fiber reinforcement. The effective thermal conductivities increase with the increase of interfacial thermal conductivity, and the effect of void volume fraction of interface becomes larger with the increase of interfacial thermal conductivity. A higher interfacial thermal conductivity have a greater effect on the effective thermal conductivities of the material than a smaller interfacial thermal conductivity.

为了预测具有随机分布的空隙缺陷的三维（3D）编织碳/碳（C / C）复合材料的有效导热率。基于渐近均匀化方法，建立了两尺度预测模型。根据材料的扫描电子显微镜观察，建立了纤维级和纤维束级的晶胞模型，并考虑了随机分布的空隙缺陷。首先预测具有空隙缺陷的纤维束的有效导热率，然后通过引入预测的纤维束的导热率，考虑基质口袋和界面中的空隙缺陷，预测3D编织C / C复合材料的有效导热率。预测的有效热导率与实验结果非常吻合，证明了两尺度预测模型的有效性。然后进行参数研究，以分析空隙体积分数和界面热导率对已开发模型的预测的影响。结果表明，空位缺陷的随机分布对有效热导率的影响很小，而空位体积分数对有效热导率的影响很大。导热系数通常随空隙体积分数的增加而线性下降，并且基质囊的空隙体积分数的影响大于纤维增强材料的影响。有效导热系数随界面导热系数的增加而增加，随着界面热导率的增大，界面空隙率的影响增大。较高的界面热导率比较小的界面热导率对材料的有效导热率有更大的影响。