A Vibration Technique For Space Shuttle Tiles Bond Assessment .1. Modeling

This paper presents a novel technique that combines laser-based vibration measurement and finite element modeling to evaluate the bond condition of the thermal protection system tiles of the Space Shuttle orbiter. This technique is based on characterizing the response of tiles when excited by audible acoustic energy. Finite element models for the assemblies attached to the orbiter aluminum skin are first developed. The tiles\u27 eigenvalues and eigenvectors are determined. Then frequency responses of tiles excited by simulated sound pressure are computed. The computed frequency response at selected points of a partially bonded the indicates a decrease in its natural frequencies. This is used to quickly identify the disbonded tiles. However, the exact size and location of the disbond are determined from the computed rigid-body modes of the tile. A companion paper presents the experimental results of test panels that are obtained by a laser rapid scan system and shows excellent agreement between the finite element and experimental results. These results demonstrate that experimental modal analysis, when combined with finite element analysis, can successfully be used as a reliable nondestructive, non-contact technique for the bond assessment