"Joining of Dissimilar Materials for Hypersonic Thermal Protection Systems" 

Ryan Carr, MSE PhD Candidate 

Advisor: Professor Rod Trice.

ABSTRACT

Thermal protection systems (TPS) are critical for protecting hypersonic vehicles from the environment created during flight, with surface temperatures up to 2000˚C expected due to aerodynamic heating. TPS are designed to withstand this heating, protecting and shielding the underlying structure of the aircraft. Due to their high temperature properties, materials used in TPS are primarily ceramic matrix composites (CMCs) and ultra-high temperature ceramics (UHTCs). With multiple TPS materials being used in the airframe, there is a need to bond these dissimilar materials that can withstand the hypersonic environment. Metallic brazes and mechanical fasteners are commonly used to join TPS materials, however, there are challenges associated with their use. These methods limit operating temperatures and increase vehicle weight and are both prone to failure due to thermal expansion. In this work, we propose a novel method for jointing TPS materials using a silica-based glass. The method is shown to successfully join both C/SiC and 2D C/C composites to Si3N4, as well as 3D C/C to C/SiC. Surface treatments for bonding with the C/C composites were developed. Two joint geometry configurations, a pinned lap and tongue and groove, were investigated. Mechanical properties for these joints were obtained through flexure testing at room temperature and an elevated temperature.