Structural buckling failure due to high external hydrostatic pressure is a major
consideration in designing rings and long cylindrical shell-type structures. This
paper presents a direct approach for enhancing buckling stability limits of
thin-walled rings/long cylinders that are fabricated from multiangle fibrous
laminated composite lay-ups. The mathematical formulation employs the
classical lamination theory for calculating the critical buckling pressure,
where an analytical solution that accounts for the effective axial and flexural
stiffness separately as well as the inclusion of the coupling stiffness terms
is presented. The associated design optimization problem of maximizing
the critical buckling pressure has been formulated in a standard nonlinear
mathematical programming problem with the design variables encompassing the
fiber orientation angles and the ply thicknesses as well. The physical and
mechanical properties of the composite material are taken as preassigned
parameters. The proposed model deals with dimensionless quantities in order to
be valid for thin shells having different thickness-to-radius ratios. Useful
design charts are given for several types of anisotropic rings/long cylinders
showing the functional dependence of the buckling pressure on the selected
design variables. Excellent results have been obtained for cases of filament
wound rings/long cylinders fabricated from three different types of materials:
-glass/vinyl-ester,
graphite/epoxy and
-glass/epoxy.
It was shown that significant improvement in the overall stability level can be
attained as compared with a baseline shell design. In fact, the developed
methodology has been proved to be a useful design tool for selecting an optimal
stacking sequence of a thin-walled anisotropic ring/long cylinder having arbitrary
thickness-to-radius ratio.
