PSI - Issue 50

V.G. Degtiar et al. / Procedia Structural Integrity 50 (2023) 40–49

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

© 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the MRDMS 2022 organizers Keywords: flight vehicles; C-C composites; surface roughness; electron microscopic study; X-ray diffraction study; distribution of voids; ablation of materials © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under responsibility of the scientific committee of the MRDMS 2022 organizers 1. Influence of structural inhomogeneities of C-C composites on change in FV shapes during the mass ablation along a flight trajectory When estimating changes in FVs shapes caused by the TPS (made, in particular, of C-C composites) mass ablation, methods described by Znamenski (1978) and Pchyolkin (2014) are applied. Surface roughness, which equivalent parameters are used to estimate a zone of laminar/turbulent transition in the boundary layer and gains of heat exchange, has substantial impact on heat exchange, Pchyolkin (2014). Under command and direct participation of authors of the present paper a complex of methods of accounting for structural inhomogeneities of TPS C-C composite elements to estimate the roughness parameters and ablation rates of materials, and corresponding methods of measuring and processing of the needed structural parameters of C-C composites, Kostin (2004), Degtiar et al. (2014), Degtiar et al. (2016), Degtiar et al. (2018), Degtiar et al. (2019), Degtiar, Saveliev et al. (2016), Degtiar et al. (2020), was developed. On ablated surfaces of TPS C-C composite elements there appears a regular pattern of large scale roughness (Fig. 1, 2) due to different rates of linear ablation of reinforcing elements and the graphitized matrix. Since the geometry of C-C composite frames is well known, the number of elements of large-scale roughness per unit area in the vicinity to a reference point and their geometrical parameters can be estimated. Large-scale roughness governs the basic level of equivalent sandy-grained roughness. One more factor impacting the equivalent roughness is outcropping of both reinforcing elements and the graphitized matrix of pores, shells, and other defects. They form the secondary fine-grained roughness. A C-C composite graphitation degree also influences their ablation rate. Moreover, C-C composite samples and parts can have a misalignment of the frame structure relative to the FV longitudinal axis that results in asymmetry of the distribution of roughness and therefore asymmetry of ablated shapes.

Fig. 1. Outcropping of reinforcing elements of a C-C composite sample of the 4KMS-L type upon fire tests in conditions close to flight of a supersonic FV.