AIAA-21689-222 - AIAA JOURNAL Vol. 45, No. 3, March 2007...

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Crack-Induced Effects on Aeroelasticity of an Unswept Composite Wing Kaihong Wang and Daniel J. Inman Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24060-0261 DOI: 10.2514/1.21689 Crack-inducedchangesinthe aeroelastic boundaries ofan unswept composite wingareinvestigated. Thebending- torsion couplings due to the unbalanced laminates and offset of the center of gravity are incorporated into the equation of motion. The edge crack, modeled with the local exibility concept, introduces additional boundary conditions at the crack location. The fundamental modes of the intact and cracked beam are used in Galerkin s method, and the approximate solution for utter and divergence speeds is obtained with steady and quasi-steady aerodynamicforces applied. Changesin utter anddivergence speeds(with respect tothecrack ratio anditslocation, along with the ber orientation) are compared. In many cases, the existence of an edge crack imposes detrimental effects on the aeroelastic boundaries, although it may increase the utter and/or divergence speed when bers are orientated at certain angles. The results may help composite wing designers in their aeroelastic tailoring and structural engineers in designing damage prognosis tools to predict the health status of composite wing structures. Nomenclature a = crack width b = beam width C L = lifting coef cient c = beam thickness EI = bending stiffness parameter GJ = torsional stiffness parameter H ± ± ² = transverse displacement h ± y;t ² = transverse displacement of the reference axis I cg = polar mass moment of inertia per unit length about the center of gravity K = bending-torsion coupling parameter L = lifting force, positive upward l = beam length l c = crack location M = pitching moment, positive nose up M ± ± ² = bending moment m = mass per unit length S cg = offset of the center of gravity S ± ± ² = shear force T ± ± ² = torsional moment U = speed of an incompressible air uid x o = reference axis location ± ± ± ² = cross-sectional rotation ² = ber angle ³ = nonzero constant ² ± ± ² = twisting angle ´ ± ² = twisting angle of the reference axis Introduction F IBER-REINFORCED composite materials have been increas- ingly used in airplane design with many advantages, such as the high strength-to-weight and stiffness-to-weight ratios and the anisotropic nature in favor of aeroelastic tailoring. Aeroelastic tailoring usually involves the design optimization of a lifting surface to achieve desired aeroelastic responses, such as the maximizing of utter and divergence speeds and the improvement of lift and control effectiveness. As one of the failure modes for the high-strength materials, crack initiation and propagation due to the manufacturing process or fatigue and impact loading during service has long been an important topic in composite and fracture mechanics communities [1]. It is also recognized that composite wing designers need to be aware of possible damage conditions at the beginning of a design involving the aeroelastic tailoring [2,3].
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AIAA-21689-222 - AIAA JOURNAL Vol. 45, No. 3, March 2007...

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