Fracture Behavior of Low‐Density Fibrous Ceramics

Abstract

It was established that subcritical crack growth occurs in the silica fiber‐based tiles that are currently in use as part of the thermal protection system (TPS) of the Space Shuttle. By measuring the tensile strength distribution and the subcritical crack‐growth parameters, it was possible to predict the material's behavior during proof‐testing. A similar time dependence of dynamic strength was also found for structural systems using this ceramic tile, suggesting that the ceramic is controlling their strength behavior. It was possible, therefore, to predict the influence of the proof testing currently in use for the Shuttle. These predictions were found to be in reasonable agreement with the experimentally determined strength distributions after proof‐testing. This study confirmed that proof‐testing and tile densification should lead to improved reliability of the TPS. The research further suggests that the subcritical crack‐growth behavior in these fibrous tiles is simiilar to that observed in bulk glass of similar composition and that failure occurs by the tensile fracture and fragmentation of individual fibers.