Ablation of the carbon/carbon composite nozzle-throats in a small solid rocket motor

Ablation of needled carbon/carbon (C/C) composite nozzle-throats was studied by hot-fire testing in a small solid rocket motor. The composition of the combustion gases was estimated by principle of free energy minimum. The ablation morphology was investigated by scanning electron microscopy. The ablation mechanism of C/C composites was also studied. The results showed that the ablation performance of C/C composites was determined by mechanical breakage of fibers/matrix together with thermal chemical ablation from the heterogeneous reactions on the throat surface. The mechanical breakage of fibers/matrix dominated the ablation of the composites at high pressure based on the calculated ablation rate. Cone-shaped fibers were formed after ablation in high fiber density area; but in low fiber density area, the fibers were peeled off because of the weakened strength after ablation. Meanwhile, the matrix around the fiber bundles was ablated into a shell shape, while the matrix between the cone-shaped fibers might be blown away by the combustion gases. Oxidation of C/C composites led to the formation of the cone-shaped fibers and shell-shaped matrix, as well as the loss of matrix between the cone-shaped fibers. The fiber/matrix fragments on the ablation surface were caused by the mechanical breakage.