Wave Propagation in Rib-Stiffened Structures: Modeling and Experiments

This work focuses on the analysis of wave propagation in rib-stiffened structures as it is related to Structural Health Monitoring (SHM) methods. Current satellite validation tests involve numerous procedures to qualify the satellite for the vibrations expected during launch, and for exposure to the space environment. SHM methods are being considered in an effort to truncate the number and duration of tests required for satellite checkout. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure, which is then received by a sensor. The received waves are evaluated over time to detect structural changes. Thus far, this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Complex isogrid reinforcements within the satellite panel significantly affect any conclusions that can be made about the arriving waves. For this purpose, an experimental and numerical study of wave propagation within rib-reinforced plates has been undertaken. Wave propagation was modeled using finite element software. These results were analyzed for an understanding of dispersion within the structure, particularly how the group velocity and mode conversion are affected by the rib interaction. Experiments were carried out to validate the model and gain further insight into the wave propagation phenomena in the structure. The analysis indicates that mode conversion plays a significant role in the first wave arrival, although this can be accounted for through proper frequency selection, and signal analysis. A range of excitation frequencies which are most appropriate for the structure are presented.