20 March 2006 Validating finite element models of composite aerospace structures for damage detection applications
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Abstract
Carbon-fiber-reinforced-polymer (CFRP) composites represent the future for advanced lightweight aerospace structures. However, reliable and cost-effective techniques for structural health monitoring (SHM) are needed. Modal and vibration-based analysis, when combined with validated finite element (FE) models, can provide a key tool for SHM. Finite element models, however, can easily give spurious and misleading results if not finely tuned and validated. These problems are amplified in complex structures with numerous joints and interfaces. A small series of all-composite test pieces emulating wings from a lightweight all-composite Unmanned Aerial Vehicle (UAV) have been developed to support damage detection and SHM research. Each wing comprises two CFRP prepreg and Nomex honeycomb co-cured skins and two CFRP prepreg spars bonded together in a secondary process using a structural adhesive to form the complete wings. The first of the set is fully healthy while the rest have damage in the form of disbonds built into the main spar-skin bondline. Detailed FE models were created of the four structural components and the assembled structure. Each wing component piece was subjected to modal characterization via vibration testing using a shaker and scanning laser Doppler vibrometer before assembly. These results were then used to correlate the FE model on a component-basis, through fitting and optimization of polynomial meta-models. Assembling and testing the full wing provided subsequent data that was used to validate the numerical model of the entire structure, assembled from the correlated component models. The correlation process led to the following average percent improvement between experimental and FE frequencies of the first 20 modes for each piece: top skin 10.98%, bottom skin 45.62%, main spar 25.56%, aft spar 10.79%. The assembled wing model with no further correlation showed an improvement of 32.60%.
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J. A. Oliver, J. A. Oliver, J. B. Kosmatka, J. B. Kosmatka, François M. Hemez, François M. Hemez, Charles R. Farrar, Charles R. Farrar, } "Validating finite element models of composite aerospace structures for damage detection applications", Proc. SPIE 6176, Nondestructive Evaluation and Health Monitoring of Aerospace Materials, Composites, and Civil Infrastructure V, 61760D (20 March 2006); doi: 10.1117/12.659350; https://doi.org/10.1117/12.659350
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