Eigen value analysis of composite hollow shafts using modified EMBT formulation considering the shear deformation along the thickness direction

Abstract

Composite hollow shafts are used in power transmission applications due to their high specific stiffness and high specific strength. The dynamic characteristics of these shafts are important for transmission applications. Dynamic modelling of these shafts is generally carried out using Equivalent Modulus Beam Theory (EMBT) and Layerwise Beam Theory (LBT) formulations. The EMBT formulation is modified by considering stacking sequence, shear normal coupling, bending twisting coupling and bending stretching coupling. It is observed that modified EMBT formulation is underestimating the shafts stiffness at lower length/mean diameter (l/dm) ratios. In the present work, a new formulation is developed by adding shear deformation along the thickness direction to the existing modified EMBT formulation. The variation of shear deformation along the thickness direction is found using different shear deformation theories, i.e., first-order shear deformation theory (FSDBT), parabolic shear deformation theory (PSDBT), trigonometric shear deformation theory (TSDBT), and hyperbolic shear deformation theory (HSDBT). The analysis is performed at l/dm ratios of 5, 10, 15, 20, 25, 30, 35, and 40 for carbon/epoxy composites, E-glass/epoxy composites, and boron/epoxy composite shafts. The results show that new formulation has improved the bending natural frequency of the composite shafts for l/dm < 15 in comparison with modified EMBT. The effect of new formulation is more significant for the second and third bending modes of natural frequencies.

Keywords

• Composite hollow shafts
• Bending natural frequency
• Modified EMBT formulation
• Thickness effect