Buckling of axially compressed cylinders with imperfect length

The load bearing capacity has been computed for axially compressed mild steel cylinders with non-uniform axial length. The initial geometric imperfection had a sinusoidal shape along the compressed edge. Computations were carried out for the radius-to-thickness ratio, 165 ⩽ R/t ⩽ 1000, the length-to-radius ratio, L/R ≡ 2.4, and the ratio of axial amplitude of imperfections to the wall thickness, 0 ⩽ A/t ⩽ 6.0.The contact problem between a rigid plate and a deformable cylinder was successfully benchmarked against experimental data on axially-perfect aluminium cylinders and also against predictions of other proprietary software. Buckling strength showed an astonishing sensitivity to axial imperfections in cylinders. Within the studied range, this could be nearly five times more severe than in the case of geometric imperfections in the shell’s generator, modelled with eigenmode type shape deviations of the same amplitude.The usual sequence of failure modes seen in compressed cylinders, i.e. asymmetric bifurcation followed by axisymmetric collapse is also no longer the case for some geometrical configurations. In particular, asymmetric bifurcation buckling can appear on the post-collapse path. This in turn can lead to ‘mode jumping’, i.e. the shell might not reach collapse and instead it can snap to the asymmetric mode at a much lower load than the predicted collapse. This has not been reported for metallic shells but it has recently been actively pursued for composite shells.