Residual thermal stresses in carbon/carbon-Zr-Ti-C composites and their effects on the fracture behavior of composites with different preforms

Carbon/carbon(C/C)-Zr-Ti-C composites were fabricated using chemical vapor infiltration and liquid metal infiltration processes. The residual thermal stress (RTS) distribution in the C/C-Zr-Ti-C composites was analyzed by Raman spectroscopy and finite element (FE) calculation. The mechanical behaviors of C/C-Zr-Ti-C composites with three types of carbon fiber preforms were tested. The results showed that there was very high compressive RTS in the fibers and high tensile RTS in the pyrocarbon (PyC) in the marginal region near the carbide. However, in the central region away from the carbide, relatively low compressive stress and tensile RTS were found in the fibers and PyC, respectively. The FE analysis showed that the introduction of carbide into the C/C composites caused a significant increase of the RTS in the PyC near the carbide, indicating that the carbide could change the RTS distribution in C/C composites. Moreover, the distribution of the RTS and its release combined with the carbide distribution and fiber architecture led to variations in the mechanical performance of composites with different preforms.