The Response of Metallic Sandwich Panels to Water Blast

Abstract

Metallic sandwich panels subject to underwater blast respond in a manner dependent on the relative time scales for core crushing and water cavitation. This article examines the response at impulses representative of an (especially relevant) domain: wherein the water cavitates before the core crushes. Three core topologies (square honeycomb, I-core, and corrugated) have been used to address fundamental issues affecting panel design. Their ranking is based on three performance metrics: the back-face deflection, the tearing susceptibility of the faces, and the loads transmitted to the supports. The results are interpreted by comparing with analytic solutions based on a three-stage response model. In stage I, the wet face acquires its maximum velocity with some water attached. In stage II, the core crushes and all of the constituents (wet and dry face and core) converge onto a common velocity. In stage III, the panel deflects and deforms, dissipating its kinetic energy by plastic bending, stretching, shearing, and indentation. The results provide insight about three aspects of the response. (i) Two inherently different regimes have been elucidated, designated strong (STC) and soft (SOC), differentiated by a stage II/III time scale parameter. The best overall performance has been found for soft-core designs. (ii) The foregoing analytic models are found to underestimate the kinetic energy and, consequently, exaggerate the performance benefits. The discrepancy has been resolved by a more complete model for the fluid/structure interaction. (iii) The kinetic energy acquired at the end of the second stage accounts fully for the plastic dissipation occurring in the third stage, indicating that the additional momentum acquired after the end of the second stage does not affect panel performance.