Damage Prognosis of Adhesively-Bonded Joints in Composite Structural Components of Unmanned Aerial Vehicles Maurizio Gobbato1, Joseph A. Oliver1, Joel P. Conte1, John B. Kosmatka1, Charles R. Farrar2 1 Department of Structural Engineering University of California, San Diego 9500 Gilman Dr., La Jolla, CA 92093-0085 email@example.com; firstname.lastname@example.org; email@example.com; firstname.lastname@example.org 2 The Engineering Institute, MS T-001 Los Alamos National Laboratory Los Alamos, NM 87545 email@example.com ABSTRACT The extensive use of lightweight advanced composite materials in unmanned aerial vehicles (UAVs) drastically increases the sensitivity to both fatigue- and impact-induced damage of their most critical structural components (such as the wings and the tail stabilizers) during service life. This may result in localized debonding, inter-ply delamination, fiber breakage and matrix cracking thereby compromising the structural performance and the level of safety of the entire vehicle. The skin-to-spar adhesive joints are considered one of the most fatigue sensitive subcomponents of a lightweight UAV composite wing with the damage progressively evolving from the wing root. A field deployable integrated hardware-software system capable of monitoring the composite UAV airframe , assessing its structural integrity, identifying a condition-based maintenance, and predicting the remaining service life of its critical components (damage prognosis ) is therefore needed. The poster illustrates a comprehensive probabilistic methodology for predicting the remaining service life of adhesively-bonded joints in laminated composite structural components of UAVs. Non Destructive Evaluation (NDE) techniques and Bayesian inference are used to (i) assess the current damage state of the system and (ii) update the probability distribution of damage extensions at multiple damaged locations. A probabilistic model for future loads and a mechanics-based damage model for the adhesive interface are then used to stochastically propagate the damage throughout the joint. Combined local (e.g., exceedance of a critical damage size) and global (e.g., flutter instability) failure criteria are finally used to compute the probability of component failure at future times. The applicability of the proposed methodology is then demonstrated by analyzing the debonding propagation along a pre-defined adhesive interface in a simply supported laminated composite beam with a solid rectangular cross section subjected to a random load. A specially developed shear deformable beam finite element with interlaminar slip along the damageable adhesive interface is used in combination with a cohesive zone model (CZM) to study the fatigue-induced degradation in the adhesive material. References  F. Lanza di Scalea, H.M. Matt, I. Bartoli, S. Coccia, G. Park, C.R. Farrar, Health monitoring of UAV skin-to-spar joints using guided waves and macro fiber composite transducers. Journal of Intelligent Material Systems and Structures, 18(4), 373-388, 2007.  D.J Inman, C.R. Farrar, V. Lopez Jr., V. Steffen Jr., Damage prognosis for aerospace, civil and mechanical systems, Wiley, 2005.
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