Modeling the oxidation, ablation, and mechanics of carbon fiber preform in thermal protection systems

The focus of this thesis is modeling the response of ablative, carbon-based thermal protection system (TPS) materials undergoing extreme heat and mechanical loading during atmospheric Earth reentry. The current state-of-the-art material is a carbon fiber reinforced phenolic composite called PICA, or phenolic-impregnated carbon ablator. Ablation of the phenolic matrix is key to transporting heat away from the shield, whereas the porous carbon-bonded carbon fiber substrate, called FiberForm, provides rigidity while still being lightweight and oxidation resistant. However, once the phenolic begins to pyrolyze, the exposed FiberForm will oxidize and become more susceptible to mass loss and mechanical degradation. Within FiberForm, there exists a porous network of carbon fibers which are bonded and fused together by a carbonaceous binder material. The challenge we address in this work is how to more accurately model oxidation and oxidation-induced mechanical response of both the fiber and binder phases in FiberForm. First, we perform molecular dynamics (MD) simulations to predict the effect of oxidation-induced pitting on the tensile behavior of carbon fiber and amorphous carbon (to represent the binder phase). In this work, we demonstrate a method to extract pit data from micrographs and superimpose them on the computational domain, and we find a significant reduction in tensile modulus for all pitted structures. We also use SPARTA, a direct-simulation Monte Carlo (DSMC) code, to develop a 1D multilayer oxidation model that can capture the competition between reaction and advection in layers of graphene. In addition, we develop and parallelize an oxidation-driven surface recession framework in SPARTA. We verify our implementation for different ablating and non-ablating test geometries in 2D and 3D. Lastly, we apply our framework to model the ablation of realistic carbon fiber geometries at flight-relevant conditions. We demonstrate its ability to accurately recreate the carbon fiber response observed for different flow regimes during reentry.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Arias, Victoria

Contributors dc:contributor

• Johnson, Harley T.
• Stephani, Kelly A
• Panerai, Francesco
• Chew, Huck Beng
• Haskins, Justin B.

• Cabon Oxidation
• Direct Simulation Monte Carlo
• Molecular Dynamics
• Porous Carbon
• Elastic Behavior

Statement dc:rights

• Copyright 2025 Victoria Arias

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129948

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129948