Change in damage tolerance characteristics of sandwich structure with a thermal protection system (TPS)

摘要

Most composite damage tolerance assessments are made on bare laminates where the impactor comes into direct contact with the outermost ply. However, structures such as those used on launch vehicles are often covered with a thermal protection system (TPS) during the majority of the life of the part. This TPS covering may change the impact characteristics of the laminate rendering damage tolerance testing on bare laminates irrelevant to the part. This study examines the composite interstage structure of the ARES I launch vehicle which is scheduled to be covered with a sprayable foam TPS after manufacture. Damage tolerance testing is performed on bare sandwich structure and sandwich structure covered with the TPS selected for use on the ARES I composite interstage. Instrumented impact, infrared thermography, visual, cross-sectional and compression after impact CAI data are compared. Results show that the TPS covering does change most of the impact characteristics of the sandwich structure. It was found that the TPS created a larger damage zone as detected by IRT, however the TPS covered specimens possessed a higher residual compression strength for a given impact energy and damage size. These results are attempted to be explained by the different damage morphology that occurs between the bare and TPS covered specimens.