Optimal Design of High Speed Rotating Graphite/Epoxy Shafts

Abstract

An important problem in the design of a high speed rotating shaft of significant span is the lateral stability. With light weight Graphite/Epoxy material it is relatively easy to meet the torsional stiffness and strength requirements using a thin walled tube, but this might lead to a shaft which is sensitive to lateral buckling. This paper will address the following question: Is it possible to increase the first natural bending frequency of the shaft through an adequate tapering of the wall thickness? A numerical procedure using a generalized criterion of optimality is outlined. The shaft was modeled using a beam formulation including shear deformation and rotary inertia. The optimization was done under constant volume constraint. Different configurations are studied for various number of plies and orientation angle. In the optimal configuration the natural frequency increased by about 21 to 44%, and the bending stress decreased by about 48 to 59%.