Bending Natural Frequencies of Circular CFRP Shafts with a Metal Core or Casing

Abstract

It has recently been shown that some carbon fiber-reinforced composite shafts with a metal core or casing are superior to all carbon fiber reinforced plastics (CFRP) or metal shafts from the viewpoint of the natural frequencies. However, it has not been reported whether or not the benefit of the metal/CFRP hybrid shafts exists in the general cases of various fiber angles, length-to-diameter ratios, material properties, and thicknesses of metal layers. In this study, the effects of a steel core or casing on the bending natural frequencies of CFRP shafts are analytically investigated. In order to calculate the frequencies, the equations of motion are obtained for metal/CFRP hybrid shafts. Several beam theories are evaluated, and differences between these theories in the prediction of the frequencies are also presented. It is found that, in certain cases, an optimum thickness of steel exists to maximize the frequencies of the steel/CFRP shafts. Parametric studies are also carried out over wide ranges of design factors, and design guidelines for the hybrid shafts are finally distilled.