Failure of composite cylinders under combined external pressure and axial loading

An experimental and theoretical investigation was carried out into the collapse behaviour of filament wound glass fibre/epoxy cylinders under combinations of external pressure and axial loading in the third quadrant of the stress plane. Samples were tested with length-to-diameter ratios from 2·5 to 20 and diameter-to-thickness ratios in the approximate range of 20 to 40. Four ratios of hoop to axial stress were employed: ∞, 2, 1 and 0·5. The theoretical study employed a special purpose finite element program to calculate first ply failure (FPF) and buckling loads for shells of revolution made from multi-layered orthotropic materials. In all cases the experimental collapse pressure was strongly influenced by the predicted buckling failure mode. For those samples predicted to fail by buckling, agreement between the model and the experimental results was excellent. With the samples predicted to undergo FPF prior to buckling it was found that the residual strength was often sufficient to permit the buckling load to be approached.