Bio-inspired hierarchical core gradation in corrugated sandwich panels: Progressive collapse and energy absorption under underwater blast loading

Abstract

Inspired by the graded distribution of vascular bundles in bamboo, this study develops bio-inspired hierarchical corrugated sandwich panels incorporating three levels of corrugation arranged in four gradation strategies: Uniform (UG), Alternate (AG), Increasing (IG), and Decreasing (DG). The dynamic response of these panels under underwater explosion loading is investigated numerically using a Coupled Eulerian-Lagrangian (CEL) framework. A parametric study spanning TNT charge masses of 10-40 g and stand-off distances of 60-120 mm evaluates the influence of core gradation on transient deformation, facesheet velocity histories, progressive core crushing, layer-wise and specific energy absorption, and failure characteristics. The results reveal that core gradation fundamentally governs the collapse mode, ranging from sequential layer-by-layer crushing in UG, through selective preferential crushing of lighter interlayers in AG and front-concentrated decelerating crushing in IG, to concurrent multi-layer deformation in DG. The DG configuration reduces front facesheet deflection by up to 46% relative to UG through a spatial separation of load-bearing and energy-absorbing functions, wherein the dense front layers provide high crush resistance and effective inertia that limit the peak facesheet velocity during the initial fluid-structure interaction, while the lighter rear layers undergo preferential plastic collapse. The findings establish that the spatial distribution of energy dissipation across the core depth, rather than its peak magnitude, governs blast mitigation efficacy, providing a transferable design principle for bio-inspired functionally graded sandwich construction.