An Integrated Methodology for Optimizing Structural Composite Damping

An Integrated Methodology For OptimizingStructural Composite DampingD.A. Saravanos*, and C.C. Cbamis**National Aeronautics and Space AdministrationLewis Reserch CenterCleveland, Ohio 44135ABSTRACTA method is presented for tailoring plate and shell composite structures for optimalforced damped dynamic response. The damping of specific vibration modes is optimizedwith respect to dynamic performance criteria including placement of natural frequenciesand minimization of resonance amplitudes. The structural composite damping is synthe-sized from the properties of the constituent materials, laminate parameters, and structuralgeometry based on a specialty finite eIement. Application studies incIude the optimiza-tion of laminated composite beams and composite shei1s with/_ber voIume ratios and plyangles as design variabIes. The results illustrate the signit_cance of damping tailoring tothe dynamic performance of composite structures, and the effectiveness of the method inoptimizing the structural dynamic response.INTRODUCTIONFiber composite materials are broadly utilized in light-weight structures, as they read-ily provide superior specific modulus and strength. In addition to stiffness and strength,polymer-matrix composite materials provide higher material damping than most metals be-cause of their "viscoelastic" matrix and heterogeneity. High specific stiffness and strengthare sufficient conditions for improved static performance, but they do not always ensureimproved dynamic performance. Passive structural damping is also a crucial dynamic prop-erty in vibration and sound control, as it generalJy improves resonance phenomena, settlingtimes, and fatigue life. Composite materials are primarily targeted for structures requir-ing good dynamic performance, such as engine, aircraft, and space structures. Therefore,the inherent damping capacity of composites becomes a significant design factor, makingpolymer-matrix fiber composites even more attractive as structural materials.*National Research Council--NASA Research Associate.**Senior Research Scientist.