LARGE DEFORMATION BEHAVIOUR OF THIN MILD STEEL RECTANGULAR PLATES SUBJECTED TO UNDERWATER EXPLOSION LOADING UNDER AIR AND WATER BACKED CONDITIONS

Abstract Marine vehicles in their operation as military vehicle are susceptible for underwater explosion from mines, torpedo etc. The damage inflicted on such structures made of ductile materials can be large deformation, tearing, rupture etc. It is imperative to design such structures for withstanding explosive loads. The damages inflicted will be mostly localized between the frames and stiffener, which can be considered as plate clamped at the edges. Hence, an attempt has been made in this paper to study the localized deformation of thin mild steel plates subjected to underwater explosion through limited explosion bulge test using small explosives. The experiments exhibited Mode I: large deformation, Mode IIa: Partial tensile tearing, Mode IIc: central rupture and Counter Intuitive Behaviour (CIB). The problem is simulated numerically using LS DYNA nonlinear finite element code considering fluid – structure interaction and the results compared with experiments. Based on the confidence gained for the air backed conditions, the analysis is extended to water backed (fully filled, 75% filled, 50 % filled) conditions and results obtained for the large deformation behaviour for various conditions are presented. The results indicate that the large deformation behaviour considerably reduces the central permanent deformation under water backed conditions compared to air backed conditions due to the fact that part of shock wave gets transmitted to the water medium behind the plate in water backed conditions.