"Stretchable Thermal Protection System for Morphing Hypersonic Vehicles" 

Nathan Misenheimer, MSE PhD Candidate 

Advisor: Professor Rodney Trice

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ABSTRACT

The development of morphing hypersonic vehicles requires revolutionary thermal protection materials that combine ablative performance with mechanical flexibility. In hypersonic environments, compression of shock waves creates extreme heating conditions where oxygen dissociation produces reactive atomic oxygen species, significantly accelerating material degradation through oxidation. Traditional ultra-high temperature ceramics (UHTCs) provide excellent ablation resistance through complex oxidation pathways and self-healing mechanisms, where controlled oxidation products seal structural flaws and channels formed during material removal. Multi-phase ceramic systems demonstrate superior performance over single-phase coatings by exploiting synergistic effects between phases, achieving near-zero linear ablation rates in temperatures up to 3,273 K. Self-healing occurs through two mechanisms: oxidation-based healing utilizing volume expansion of oxide products like 𝑆𝑖𝑂2 (80% volume increase from SiC), and precipitation-based healing that functions synergistically with oxidation processes. However, these high-performance ceramics remain inherently brittle with fracture toughness values <10 MPa·√𝑚 and critical flaw sizes of 10-100 𝜇𝑚. Flexible ceramics overcome brittleness through two approaches: nanofiber architectures with diameters below critical flaw sizes enabling strains over 70%, and hierarchical porous structures like aerogels achieving 85% recoverable compressive strain through engineered pore networks. The fundamental challenge lies in the inverse relationship between porosity and ablative performance—the same structural features that enable flexibility also promote oxygen ingress and reduce available ablative material. Research into stretchable ablatives for fire protection applications indicates that tensile strain increases mass ablation rates and reduces thermal protection effectiveness, suggesting this challenge extends beyond aerospace applications. The solution requires unprecedented integration of nanofiber flexibility with proven anti-oxidation chemistry.