"ENERGY ABSORBING CERAMICS FOR ROTATING DETONATION ENGINE" 

Benjamin Lam, MSE PhD Candidate 

Advisors. Prof. Rodney Trice & Carlos Martinez

ABSTRACT

Rotating detonation engines (RDEs) represent a highly promising advancement in propulsion technology, offering superior thermodynamic efficiency and power density compared to conventional combustion systems. However, the extreme environment within the RDE annular combustion chamber — characterized by high-frequency, high-amplitude detonation pressure waves, intense thermal gradients, and repeated mechanical shock loading — imposes severe structural and thermal demands on combustor wall materials. Ceramic materials are attractive candidates for RDE inner and outer combustor bodies owing to their thermal stability; however, their inherent brittleness and linear elasticity result in the direct transmission of detonation-induced energy, accelerating crack initiation and propagation, contributing to structural failure. This study investigates the design, processing, and thermomechanical characterization of energy-absorbing ceramic composites employing borosilicate glass as a secondary dispersed phase within a crystalline mullite matrix. At temperatures above the glass transition temperature of the borosilicate phase, a substantial decrease in viscosity facilitates viscous energy dissipation. The glass secondary phase transitions to a viscoelastic mechanical response, providing enhanced damping capacity within the crystalline mullite matrix. As a secondary phase, up to 20 vol% of borosilicate glass spheres of varying sizes is mixed into mullite powder, then hot pressed to produce the final parts. The influence of the size and volume fraction of the glass spheres, as well as the microstructure of the bulk part, on damping and modulus as a function of temperature were studied using the impulse excitation technique (IET). Results indicate that all three variables — glass sphere size and volume fraction, and microstructure of the specimen — produce measurable effects on the viscoelastic response of the composite. The volume fraction of the glass phase was identified as the dominant factor governing damping behavior, while microstructural features influenced both elastic modulus and damping. The size of the borosilicate spheres had little effect on the system. In parallel, the feasibility of digital light projection (DLP)-based additive manufacturing was explored as a fabrication route for a SiO₂/mullite material system. Successful ink development, printing, and post-processing demonstrates the viability of additive manufacturing as a scalable manufacturing pathway for complex geometries. Collectively, these results validate both the theoretical basis and practical manufacturability of energy-absorbing ceramics for RDE applications, with direct implications for extended combustor service life and enhanced structural durability.