Impact Loads Identification in Standoff Metallic Thermal Protection System Panels

This article describes two experimental approaches for the identification of transient impact loads applied to a metallic composite thermal protection system (TPS) panel. The critical nature of the TPS to the survival of the vehicle and crew warrants the development of a technique that can detect, quantify, and locate transient impact loads. This information will provide an opportunity to identify specific panels that are more or less prone to damage from transient impacts. Furthermore, a historical database of impact loads encountered can be retained for use in the development of statistical models that relate impact loading to panel life. The two techniques presented herein are a physics-based approach, where the panel is assumed to behave as a rigid body at low frequencies, and an inverse frequency response approach, where the system impedance matrix is measured, from which the loads acting on the panel can be estimated using the measured response. The validity of approaches is verified experimentally, and it is shown that the inverse frequency response method is capable of detecting, locating, and quantifying transient impact loads to a high degree of accuracy.