A simple criterion to evaluate the rupture of materials in ship collision simulations

Abstract The paper is dedicated to enhance the industry practice in collision simulations of ship structures when only limited time and material data are available. The idea is to establish a simple, but effective procedure to determine the ‘critical failure strain’ as a function of coarse mesh sizes, so as to predict the critical energy to be absorbed during the impact. For this reason, more complicated effects, such as strain-state dependence, strain concentration on the lateral stiffening, welding, as well as accurate deformation mechanisms, are omitted. A new expression is introduced to estimate the failure strain of coarse meshed ship structures struck by an indenter with hemispherical shape where the ship side or bottom sustains local penetration during a bulbous bow collision or stranding. The expression is valid for mild and high strength steels, accounts for the size of the elements, and is derived from finite element simulations of coarse meshed plates punched until the onset of necking, which critical point is first determined by using fine meshed plates. This ‘simple’ criterion is validated against reported experiments of 3 stiffened plates and 6 double-hull structures quasi-statically punched by an indenter. For the 6 double-hull specimens evaluated here, the absorbed energy at the end of the impact event is predicted with sufficient accuracy when a coarse mesh of size 10 times the plate thickness is used (the difference is about 10%).