The meso-structure is important in predicting mechanical properties of the three-dimensional (3D) braided composite. In this paper, the internal structure and porosity of threedimensional full five-directional (3DF5D) braided composite is characterized at mesoscopic scale(the scale of the yarns) using micro-computed tomography (micro-CT) non-destructively. Glass fiber yarns as tracer are added into the sample made of carbon fiber to enhance the contrast in the sectional images. The model of tracer yarns is established with 3D reconstruction method to analyze the cross-section and path of yarns. The porosities are reconstructed and characterized in the end. The results demonstrate that the cross sections of braiding yarns and axial yarns change with the regions and the heights in one pitch of 3DF5D braided composites. The path of braiding yarns are various in the different regions while the axial yarns are always straight. Helical indentations appear on the surfaces of the axial yarns because of the squeeze from braiding yarns. Moreover, the porosities in different shapes and sizes are almost located in the matrix and between the yarns.

细观结构对于预测三维（3D）编织复合材料的机械性能至关重要。本文采用无损显微计算机断层扫描（micro-CT）技术在细观尺度（纱线尺度）上表征了三维全五向（3DF5D）编织复合材料的内部结构和孔隙率。将玻璃纤维纱作为示踪剂添加到碳纤维编织成的试样中，以增强截面图像的对比度。利用3D重建方法建立了示踪纱线的模型，以分析纱线的横截面和路径。最后对孔隙率进行了重建并进行了特征化。结果表明，编织纱线和轴向纱线的横截面随3DF5D编织复合材料的一个节距中的区域和高度而变化。编织纱线的路径在不同区域是不同的，而轴向纱线始终是直的，但由于编织纱线的挤压，螺旋状的凹痕出现在轴向纱线的表面上。此外，不同形状和尺寸的孔隙几乎分布于纱线之间基体中。