The influence of deformation limits on fluid–structure interactions in underwater blasts

•The classical FSI problem is revisited for a fully clamped elastoplastic beam.•Beneficial effects of FSI depends on the transverse deflection and time to detachment.•Impulse transmitted is reduced by increasing aspect ratio in mode I deformation.•Decreasing aspect ratio always reduces impulse transmitted in modes II and III. This paper revisits a classical fluid–structure interaction (FSI) problem on the momentum and energy transfer to a structure from an underwater blast. Hitherto, the majority of analytical models assume a rigid (non-deformable) and free-standing (unsupported) structure where resistance to its translational motion – apart from that offered by its inertial mass – comes from ‘ad-hoc’ backing spring(s) introduced to simulate compression of the fluid medium and/or the resistance to transverse deformation encountered by a real structure. These limitations/assumptions are relaxed in this paper by adopting a physically realistic fully-clamped ductile beam system that takes into account large elasto-plastic deformation, limits to material deformation, boundary compliance and boundary failure; the analytical framework was developed previously by Yuan et al. (2016). By coupling the fluid (water) domain to the analytical model of the ductile beam system, the momentum and energy transferred by the blast wave are critically re-evaluated for non-impulsive loading régime; in particular, on how the beam’s deformation mode and boundary compliance affects fluid and structure interaction, up until the point of complete beam detachment from its supports. Detailed finite-element models were also developed to simulate the interactions between the fluid and structural beam where predictions were in good agreement with those by the analytical model. Sensitivity analyses were carried out that offer new insights on the influence of the beam’s aspect ratio and inertial mass.