Department: Structural Engineering
Name: Joseph A. Oliver
Email: jaoliver @ ucsd.edu
Grad Year: 2008
Fiber-reinforced composites materials exhibit excellent performance characteristics, such as high specific stiffness and strength, tailorable properties, and the ability to form large complex shapes without secondary joining procedures. However, their use in primary aerospace structures use is complicated by internal damage modes and a lack of yield mechanisms before complete failure. Damage, which can be understood as a localized decrease in stiffness, alters the vibration characteristics of the entire structure; analysis of the global dynamic behavior of a structure therefore has the capability to give insight into the damage state of the system. With this in mind, work is underway at UCSD?s CASL to develop a vibration-based system for damage-detection and structural health monitoring (SHM) of composite aerospace structures, in particular for unmanned aerial vehicles (UAV). UAVs offer the perfect platform for SHM development: they rely heavily on composites for primary structures, are operated to the limits of their design capacity, and are subject to relaxed regulations compared to structures which support human life, meaning that hardware testing and implementation is much more accessible. Four all-composite test pieces emulating wings from a lightweight all-composite UAV have been developed and manufactured to support SHM research. Two wings are undamaged and two have damage built into the main spar-skin bondline; one of each type also has a set of sensors embedded into its internal structure. This combination of damage and hardware allows realistic data-acquisition, and study of the relative impact of hardware variation compared to the changes from the damage being detected. Detailed finite element (FE) models have also been created of the four structural components of each wing as well as the assembled structures. Low-frequency (0-1000 Hz) vibration testing of the component pieces allows correlation of the FE models with the help of meta-models; the FE models are then used with data from the complete wing structures for damage detection. Combining this information with probabilistic modeling and analysis will provide a path to complete SHM?detailed real-time knowledge of structural health and estimates of life remaining.
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