Characterization of post-yield behavior of a warship grillage subject to repeated impacts

Abstract

This thesis investigates the progressive accumulation of plastic strain in the response of a uniaxially-stiffened warship grillage repeatedly impacted by a smooth, rigid, spherical indenter. An explicit, nonlinear numerical model was developed, and five distinct indentation patterns were applied over an ultra-low cycle frequency range (<50 impacts) across a range of impact velocities to characterize the grillage response. The results were analyzed to assess whether a ship structure exhibits shakedown behaviors associated with small strain plasticity and fatigue behaviors, or whether sufficient evidence exists to suggest considerations for progressive plastic accumulation (ratcheting) be made when assessing damage capacity in ship structural analysis. Impact experimentation was conducted at full-scale using a double-pendulum style impact apparatus to validate the numerical model. The experimental observations show fair agreement with the numerical simulations. It was found that at increasing levels of impact energy, the grillage response transitioned from elastic shakedown to pseudo-shakedown or ratcheting responses.