Experimental Analysis of Dynamic Deformation and Damage in Composite Sandwich Structures Subjected to Underwater Impulsive Loads

摘要

The analysis of dynamic response of sandwich structures is complicated due to material heterogeneity, complex loading conditions and competing failure mechanisms. This investigation focuses on overall structural response, deformation, damage, and energy-absorption in air-backed and water-backed/submerged composite sandwich structures. The damage and failure characteristics of individual components of the sandwich structures are studied using laser-based in-situ diagnostics and postmortem analysis. Simply-supported composite sandwich plates with varying core-densities are subjected to a range of underwater impulsive loads using a novel projectile-impact based impulsive loading facility called the Underwater Shock Loading Simulator (USLS). In-situ high-speed digital imaging and postmortem analysis are used to study the dynamic deformation and failure characteristics of individual components; focusing on the effects of loading rate, core-characteristics and material heterogeneity on structural response. In finite-element simulations, the underwater blast loading intensity is considered using the Mie-Gruneisen equation-of-state of a linear Hugoniot form and core crushing is accounted for through a modified Drucker-Prager model. Results indicate that the core-density has a significant influence on dynamic deformations and failure modes. On a per-weight basis, low-density foam cores consistently outperform high-density foam cores, undergoing lesser deflections and transmitting smaller impulses. Polymeric foams experience considerable rate-effects and exhibit extensive shear cracking and collapse under high-magnitude multi-axial underwater impulsive loads. Calculations reveal a significant difference between the response of air-backed and water-backed/submerged structures. The experiments and computations offer approaches for improving the blast mitigation capabilities of submerged composite sandwich structures in the critical parts of a ship structure like keel, turbine-blades and rudders.