Effects of preform structure on microstructure and mechanical properties of long/short fiber‐coupled C/C–SiC composites

Abstract C/C–SiC composites with four different preform structures were prepared via chemical vapor infiltration and reactive melt infiltration (RMI). The effects of preform structure on the microstructure and mechanical properties of the C/C–SiC composites were thoroughly investigated. The results indicate that the porous C/C composites with multidirectional long/short fiber‐coupling exhibited consistent pore size distribution (diameter: 5–300 µm) and periodicity pore distribution characteristics. As the effective fiber volume fraction in the loading direction of the C/C–SiC composites increased from 11.71% to 21.04%, the tensile and flexural strength significantly increased by 64.44% and 44.03%, respectively, with minimal effect on compressive and interlaminar shear properties. The introduction of Z ‐direction fiber, such as stitched structure, increased the compressive and interlaminar shear strength of the composites by 10.87% and 15.67%, respectively. A theoretical predictive model of ultimate tensile strength after modification was validated for application to the C/C–SiC composites prepared by RMI, through characterization of the volume fraction of each layered unit and the content of each component. However, the presence of defects caused by the stitched structure, such as fiber bending, occupancy, and pores, reduced tensile and flexural strength by 30.45% and 28.56%, thereby impacting the effectiveness of the predictive model negatively.