Thickness optimization for maximum buckling loads in composite laminated plates

Isotropic plates and composite laminated plates are modeled using variable thickness, shear deformable, finite plate elements. The method of feasible directions is used to determine optimal thickness distributions over the plate that yield maximum uniaxial and biaxial buckling loads. Plates that have thicknesses tailored uniaxially and biaxially are considered. Optimum isotropic plate designs indicate a complex interaction occurs between inplane load redistribution and bending/twisting stiffness redistribution during the optimization process. Optimization produces increases in uniaxial buckling loads of over 200% for isotropic plates compared to uniform plates. Much smaller improvements are possible when biaxial compressive loads are present. Composite materials also allow for increased efficiency in the redistribution of loads and stiffnesses. Improvements in both uniaxial and biaxial buckling loads of over 160% are shown possible in composite plates compared to uniform quasi-isotropic plates. The effects of transverse shear stiffness on the optimum design and corresponding buckling load for both isotropic and composite laminated plates are studied by analyzing plates with different width/thickness ratios. The improvement in the buckling loads through thickness optimization is shown to decrease as the effects of transverse shear increase.