On Shock Response of Marine Sandwich Structures Subjected to UNDEX Loading

Abstract

Survivability at sea in a hostile environment is the last line of hope for naval platforms. Research today has seen advancement of underwater explosion science along with the delivery systems such as torpedoes and underwater missiles. The evaluation of the structural response to such explosive loading and designing structures to attenuate the loading effects is of prime concern. The structural response to various impulsive loads specifically to blast loads in the elasto-plastic region will be in the form of large deformation, crack initiation and tensile tearing. The above failure modes can be predicted reasonably accurately at the design stage based on finite element modelling employing nonlinear shock analysis. In the prediction of structural response beyond elastic limit, both material and geometric nonlinearity are to be considered. The material non-linearity is generally modeled by Von Mises yield criteria and associated flow rules with isotropic hardening. The material models such as rigid plastic, elastic perfectly plastic and elasto-plastic can be used to represent the material behaviour. The geometric non-linearity is based on total or updated Lagrangian formulation. Cole [1] established useful empirical relations to model the underwater explosion (UNDEX) loading, which were the outcome of numerous experimental investigations done by the military agencies. In the present study the UNDEX load profile has been modeled as an exponentially decaying shock wave which varies spatially and transiently. An elasto-plastic model with isotropic hardening, strain rate effects and fracture criterion has been developed was used to predict and establish the failure modes in high strength (HS) and WELDOX Steel rectangular plates sandwiched with a metallic core structure, under clamped edge conditions. These models were implemented in the non-linear finite element code ABAQUS/Explicit. The present study establishes empirical relationships derived from numerical analysis of stiffened and un-stiffened plates subjected to UNDEX.