Quasi-active, minimal-sensing load and damage identification and quantification techniques for filament-wound rocket motor casings

Filament-wound rocket motor casings are being considered by the United States Army for use in future lightweight missile systems. As part of the design process, a real-time, minimal-sensing, quasi-active health-monitoring system is being investigated. The health-monitoring scheme is quasi-active because abnormal loads acting on the structure are identified passively, the input force is not measured directly, and the curve-fit estimate of the impact force is used to update the frequency response functions (FRFs) that are functions of the system properties. This task traditionally requires an active-interrogation technique for which the input force is known. The updated FRFs and the estimated impact force can then be used in model-based damage-quantification methods. The proposed quasi-active approach to health monitoring is validated both analytically with a lumped-parameter model and experimentally with a composite missile casing. Minimal sensing is used in both models in order to reduce the complexity and cost of the system, but the small number of measurement channels causes the system of equations used in the inverse problem for load identification to be under-determined. However, a novel algorithm locates and quantifies over 3000 impacts at various locations around the casing with over 98% success, and the FRF-correction process is successfully demonstrated.