Abstract

Due to the outstanding engineering properties, such as high strength/stiffness to weight ratios, capability to be stiff at one location and flexible at another location and favorable fatigue characteristics, doubly-tapered composite beam is used in the rotating structures such as helicopter rotor blades and wind turbine blades. Due to its distinct characteristics from static beam and wide range of applications, rotating beam requires a comprehensive research to understand its dynamic response. Design of mechanical components using doubly-tapered composite beams requires a better understanding of their behavior in free vibration and their dynamic instability. In the present thesis, free vibration and dynamic instability analyses of doubly-tapered rotating cantilever composite beams are conducted considering three different types of vibrations (out-of-plane bending, in-plane bending and axial). Rayleigh-Ritz approximate method based on classical lamination theory has been employed to formulate the free vibration problem and solve it. Bolotin’s method is applied to determine the instability regions. Numerical and symbolic computations have been performed using the software MATLAB. The results for natural frequencies have been validated using Finite Element Analysis (FEA) tool ANSYS. A comprehensive parametric study is conducted in order to understand the effects of various design parameters. Moreover, critical speed of doubly-tapered rotating composite beam is determined and change of critical speed due to double-tapering is investigated. Also, change in maximum deflection due to rotational velocity and double-tapering is observed in this thesis. The material chosen in this thesis for numerical calculations is NCT-301 graphite-epoxy prepreg.