Free and forced vibrations of tapered composite beams including the effects of axial force and damping

摘要

Tapered composite beams formed by terminating or dropping-off some of the plies from primary structure are being used in various engineering applications since the mid-1980s. Because of their structural tailoring capabilities, damage tolerance and potential for creating significant weight savings in engineering applications such as helicopter yoke, robot arms and turbine blades, tapered composite beams have received much attention from engineers and researchers. Design of mechanical components using tapered composite beams requires a better understanding of their behavior on free and forced vibrations. In the present thesis, free and forced vibration analysis including the effects of axial force and damping of tapered composite beams is conducted using conventional, and higher-order finite elements and the Rayleigh-Ritz method. Composite beam samples are manufactured and tested for the determination of mechanical properties and damping loss factor. Conventional and higher- order finite element formulations are established based on classical laminate theory. Since conventional finite element has limitation in obtaining accurate results with fewer elements, higher-order finite element formulation is developed considering four degrees of freedom per node (deflection, rotation, curvature and gradient of curvature) to overcome that problem. Rayleigh-Ritz method is used to obtain solutions for different boundary conditions to validate the results obtained by finite element methods. A detailed parametric study is conducted to investigate the effects of boundary conditions, laminate configurations, taper configurations, taper angle, the ratio of the length of the thick section to the length of thin section, axial force, and damping. The NCT-301 graphite-epoxy composite material is used in the experimental work, analysis, and in the parametric study.