The electrical response of refractory carbon/carbon composites to high-temperature ablation: A pathway to embedded sensing in extreme environments

Abstract

High-temperature ceramics and composites are essential for leading edges on next-generation high-speed aerospace vehicles, where the surfaces are expected to see extreme temperatures and heat fluxes. However, these materials are vulnerable to in-flight degradation arising from oxidation and ablation. Due to the extreme conditions encountered during flight, even slight changes in surface properties can profoundly affect aerodynamic performance and precipitate catastrophic failure. In-flight embedded sensing is therefore critical. Unfortunately, traditional sensors either prohibitively interfere with aerodynamics or cannot survive in-flight conditions. To overcome this challenge, we explore the material-as-the-sensor paradigm for extreme environment materials. Changes in the electrical properties of a refractory carbon/carbon (C/C) composite are used as an indicator of degradation. C/C composite strips were exposed to an oxyacetylene torch to represent oxidation and ablation expected during service, and the electrical impedance of the strips was measured before and after each exposure. It was found that ablation-induced damage has a clear impact on alternating current transport that scales with increasing exposure time and ablated volume. Equivalent circuit analyses were conducted in order to better understand the nature of ablation damage on transport characteristics; it was found that the resistance of the equivalent circuit increases with increasing torch exposure time and ablated volume. This study is an important proof-of-concept result for establishing embedded sensing techniques in next-generation extreme environments.