Abstract

Tapered composite beams are being used in various engineering applications such as helicopter yoke, robot arms and turbine blade in which the structure needs to be stiff at one location and flexible at another locations. Laminated tapered beams can be manufactured by terminating some plies at discrete locations. Different types of ply drop-off can be achieved depending on the application. Due to the variety of tapered composite beams and complexity of the analysis, no analytical solution is available at present and therefore finite element method has been used for the calculation of response. In the present thesis, the free vibration response and buckling of different types of tapered composite beams are analyzed first using conventional finite element formulation. Conventional finite element formulation requires a large number of elements to obtain acceptable results. In addition, continuity of curvature at element interfaces can not be guaranteed with the use of conventional formulation. As a result, stress distribution across the thickness is not continuous at element interfaces. In order to overcome these limitations, an advanced finite element formulation is developed in the present thesis for vibration and buckling analysis of tapered composite beams based on classical laminate theory and first-order shear deformation theory. The developed formulation is applied to the analysis of various types of tapered composite beams. The efficiency and accuracy of the developed formulation are established in comparison with available solutions, where applicable, as well as with the results obtained using conventional formulation. A detailed parametric study has been conducted on various types of tapered composite beams, all made of NCT/301 graphite-epoxy, in order to investigate the effects of boundary conditions, laminate configuration, taper angle, the ratio of the length of the thick section to the length of the thin section and the ratio of the height of the thick section, to the height of thin section.