Effect of the Atmosphere in the Ablation of Carbon-Phenolic Composites Used in Thermal Protection Systems

Abstract

Ablatives composite materials are vastly employed in rocket nozzle components and as thermal protection shields in aerospace industry. In this work, an experimental study on the influence of atmospheric pressure on the ablation of carbon-phenolic composites is performed. The composite is produced by wrapping process and used in the manufacture of thermal re-entry protections. Samples were tested in the following thermal fluxes: 0.626; 0.903; 1,376 and 1,725 MW/m 2 in the 30, 50, 70 and 90 sec exposure times in a plasma tunnel simulating the pressure of 400 Pa and compared to the results obtained in the same thermal fluxes and exposure times at atmospheric pressure. Results were also compared with a computational simulation and a simple and reliable model is proposed to express the influence of environment pressure, presenting good agreement and physical coherence. The specific mass loss rate at rarefied pressure was lower than obtained at dense atmospheric pressure but this difference decreases with the increase of the exposure time due to the process of densification of the carbonized layer. The low concentration of oxygen existing in the rarefied air pressure contributes to slow pyrolysis reaction during the ablation process

Analysis of mullite ablative properties simulated in hypersonic plasma wind tunnel / Análise das propriedades ablativas da mulita simuladas em túnel de vento plasma hipersónico

“…Part of the heat input stream is blocked by the flow of hot gases resulting from material degradation. The ablative system is generally used on vehicles Brazilian Journal of Development, Curitiba, v.7, n.9, p. 88245-88258 sep. 2021 designed for one mission only (Riccio et al, 2017;Hu et al, 2012;Bittencourt et al, 2018). The degradation of an ablative material should be an endothermic reaction such as fusion, sublimation and carbonization, based on the principle of thermal energy absorption, generating a reasonable amount of gases, resulting in thermal insulation and progressively occurring material consumption.…”

“…These matrices are one of the most common types of reinforcement used in TPS systems because in carbonization ablation their main feature is the formation of a porous skeleton where gases can flow while the degradation reaction evolves, absorbing energy and blocking heat flow. when injected into the boundary layer (Machado, 2013;Bittencourt et al, 2018). Therefore, carbon fiber reinforced (C/C) carbon arrays are used in materials in the aerospace industry due to their desirable characteristics such as high ablation and mechanical resistance, heat resistance, dimensional stability, high solvent resistance, acids and water, flame resistance, low smoke emission when material is incinerated, excellent ablative properties and low cost.…”