<title>Identification of damage in a standoff metallic thermal protection system panel subjected to combined thermo-acoustic excitation</title>

Abstract

The thermal protection system is an essential part of any launch vehicle. Standoff metallic thermal protection system (TPS) panels protect the vehicle from the hostile environment on the panel exterior; consequently, the panels are exposed to a variety of loads including high temperature thermal stresses, thermal shock, acoustic pressure, and foreign object impact. These loads can cause degradation in the health of mechanically attached metallic TPS panels in the form of, for example, face sheet buckling, deformation/cracking of standoff bolts and standoffs or wrinkling to thermal seals. In this work, two sets of experiments were performed. The first experiment aimed to partially recreate the acoustic environment that the TPS experiences during service by subjecting the panel to broadband noise broadcast from a loudspeaker. In this set of experiments, "damage" was introduced into the TPS by loosening standoff fasteners to represent cracked or warped bolts and a transmissibility-based damage index was implemented to detect and locate damage. The second experiment was designed to examine the variation in damage indices when the panel is subjected to combined thermo-acoustic loading. In this set of experiments, the panel was not subjected to any "damage"; instead, the exterior of the panel was heated with an infrared heat lamp while being excited by acoustic noise. It is demonstrated that the transmissibility-based damage indicator is a viable method for detecting and locating damage in the TPS panel. It is also shown that damage present in the panel may become more or less identifiable while the system is subjected to thermal loading. This paper was approved for unlimited public release on February 18, 2005; LA-UR-05-1192.