Hoop and axial plastic buckling modes of submerged cylindrical shells subjected to side-on underwater explosion shock wave

Cylindrical shells are widely used in marine structures from small-sized pipes to various immersed containers and large submarines. Dynamic plastic buckling of the shells could be caused by underwater explosion (UNEX) loads in industrial accidents or hostile attacks. Influential factors including non-dimensional hull shock factor reflecting the resilience of the material to shock intensity, slenderness ratio, localised ring stiffener and endcap are identified. Their impacts on the dynamic buckling modes are discussed relied on the finite element investigations. The results show that the global hoop and axial buckling modes are mainly determined by the hull shock factor and slenderness ratio, respectively. With the increase of hull shock factor, i) back-side buckling, ii) back- and front-side buckling with dominant buckles at the back-side, iii) back- and front-side buckling with dominant buckles at the front side, and iv) overall buckling with very large buckles at the front-side originating from the priority buckling modes can be observed in the circumferential direction. The competition between the front- and back-sides buckling is attributed to their different buckling mechanisms. The former one is caused by shock transmitted from the explosion source through the fluid, whereas the later one is due to striking of the structural hoop stress waves propagated from the front-side via the shell itself. Axial buckling modes consisted of primary and potential buckles alternating in the axial direction could be triggered for a large slenderness ratio, but be concealed by localised buckling modes for small slenderness ratio. The localised buckling modes are controlled by the ring-stiffener and endcap, because they alter the continuity of compression potential of shells.