High-speed digital imaging and computational modeling of dynamic failure in composite structures subjected to underwater impulsive loads

•Novel experiments are carried out to quantify response of sandwich structures to water-based impulsive loading.•Experiments and simulations account for a range of structure attributes and different water–structure contact conditions.•Analyses focus on rigidity, core compression, and impulsive transmission of different structures with equal mass.•Results reveal optimal core density/height combination for both water-backed and air-backed loading.•Scaling relations are developed to provide guidance for design of structures to maximize blast resistance.

The load-carrying capacity of composite structures under water-based impulsive loads is evaluated in relation to different core materials and load intensity. The analysis focuses on the role of core density and the effect of varying structural attributes and environmental conditions on deformation and failure mechanisms in monolithic as well as sandwich composites. The structures analyzed are simply supported planar composites with PVC foam cores and E-glass/vinylester facesheets. For the analysis carried out, the material properties of the sandwich cores are varied while the total mass is kept constant. The structures are subjected to impulsive loads of different intensities using a novel new projectile-impact-based facility called the Underwater Shock Loading Simulator (USLS). In-situ high-speed digital imaging and postmortem analysis are used to study the deformation and failure of individual components, focusing on the effects of loading intensities, failure modes and material heterogeneity. Depending on the loading rate, shear cracking and/or collapse are the primary failure modes of the polymeric foam cores. Core density and height also significantly influence the response and failure modes. On a per unit weight basis, structures with low density cores consistently outperform structures with high density cores because the former undergo smaller deflections, acquire lower velocities and transmit a smaller fraction of incident impulses. Scaling relations in the form of deflection and impulse transmitted as functions of core density and load intensity are obtained to provide guidance for structural design.