Dynamic behaviour of pretwisted metal matrix composite blades

In this first attempt, a unified, consistent and accurate numerical solution is obtained for the dynamic behaviour of a metal matrix composite (MMC) blade. The MMC blade is made of Titanium (Ti6Al4V) and reinforced with Silicon Carbide (SiC) fibers. The present nonlinear formulations take into account airfoil profile of the blade, profile pretwist angle, fiber orientation, reinforcement volume fraction, coupling of bending and torsional displacement fields, and centrifugal stiffening. Three aspects of the work are considered. The first is concerned with the development of a unified approach to describe the blade's dynamic behaviour. The second with the determination of the effective properties of the MMC blade using micromechanical homogenisation. The third with the discretization of the displacement field and its treatment using Gaussian quadrature. The developed model is used to examine the effect of angle of pretwist, blade thickness, fiber volume fraction and fiber orientation on the dynamic response of the blade. The results reveal that a significant increase in the natural frequencies of the blade can be obtained with the reduction of its weight as a result of the SiC reinforcement. They also show that the bending and torsional natural frequencies are governed by the pretwist angle.