Measurements of parameters of structures of C-C composites to ensure the computation of change in FV shape and aerodynamic characteristics

Abstract

The paper provides a designed under the supervision and with the participation of authors of the paper complex of methods of accounting for structural inhomogeneities of elements of a Thermal Protection System (TPS) made of C-C composites used to estimate ablated shapes of high-speed Flight Vehicles (FVs) and corresponding methods of measuring and processing of the needed structural parameters of C-C composites. During the mass ablation along a flight trajectory reinforcing elements and a graphitized matrix ablate differently, and there appears primary large-scale roughness on the surface. Moreover, pores, shells, and other fine-grained inhomogeneities outcrop forming the secondary finely divided roughness. Roughness impacts heat exchange, and summary equivalent roughness parameters are used to estimate FVs ablated shapes. A C-C composite graphitation degree that is defined with the X-ray diffraction study also influences an ablation rate. The density of materials is linearly related to their porosity, and for a number of currently in use and promising materials the density distributions were studied using computer tomography as well as the distribution of pores, shells, and other fine-grained inhomogeneities over volume of TPS elements was examined with electron microscopes. X-ray diffraction studies of the C-C composites were also carried out. Comparative computations of ablated shapes and aerodynamic characteristics of a model cylindrical FV with applied TPS elements of the examined C-C composites were performed with the use of obtained results of tomography, electron microscopic and X-ray diffraction studies.