Response of metallic pyramidal lattice core sandwich panels to high intensity impulsive loading in air

Kumar P Dharmasena,Haydn N.G Wadley,Keith Williams,Zhenyu Xue,John W Hutchinson

doi:10.1016/j.ijimpeng.2010.10.002

Kumar P Dharmasena, Haydn N.G Wadley + Show 3 more

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Small scale explosive loading of sandwich panels with low relative density pyramidal lattice cores has been used to study the large scale bending and fracture response of a model sandwich panel system in which the core has little stretch resistance. The panels were made from a ductile stainless steel and the practical consequence of reducing the sandwich panel face sheet thickness to induce a recently predicted beneficial fluid–structure interaction (FSI) effect was investigated. The panel responses are compared to those of monolithic solid plates of equivalent areal density. The impulse imparted to the panels was varied from 1.5 to 7.6 kPa s by changing the standoff distance between the center of a spherical explosive charge and the front face of the panels. A decoupled finite element model has been used to computationally investigate the dynamic response of the panels. It predicts panel deformations well and is used to identify the deformation time sequence and the face sheet and core failure mechanisms. The study shows that efforts to use thin face sheets to exploit FSI benefits are constrained by dynamic fracture of the front face and that this failure mode is in part a consequence of the high strength of the inertially stabilized trusses. Even though the pyramidal lattice core offers little in-plane stretch resistance, and the FSI effect is negligible during loading by air, the sandwich panels are found to suffer slightly smaller back face deflections and transmit smaller vertical component forces to the supports compared to equivalent monolithic plates.

Highlights

Sandwich panel structures made from ductile metals with square and triangular honeycomb cores have shown promise for mitigating some of the effects of localized shock loading in air and water [1, 2]
Recent experiments have shown that the back face deflections of centrally loaded edge clamped sandwich panels can be significantly less than equivalent areal density solid plates subjected to the same loading [3,4,5,6,7,8]
The study shows that efforts to use thin face sheets to exploit fluid-structure interaction (FSI) benefits are constrained by dynamic fracture of the front face and that this failure mode is in part a consequence of the high strength of the inertially stabilized trusses

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Introduction

Sandwich panel structures made from ductile metals with square and triangular honeycomb cores have shown promise for mitigating some of the effects of localized shock loading in air and water [1, 2]. Recent experiments have shown that the back face deflections of centrally loaded edge clamped sandwich panels can be significantly less than equivalent areal density solid plates subjected to the same loading [3,4,5,6,7,8] Theoretical assessments indicate this beneficial effect arises from two phenomena: a reduction in the impulse acquired by the sandwich panel front face as a result of a fluid-structure interaction (FSI) effect [3,4,8,9,10] and the higher flexural stiffness and strength of the sandwich. It has been experimentally shown that the forces transmitted to supports when rigid back supported sandwich panels are impulsively loaded in water are significantly less than equivalent solid plates [11,12,13,14] These reductions arise from a combination of beneficial FSI effects (which reduce the transmitted impulse) and a low core crushing stress. Analogous effects are anticipated to be present in edge supported panels subjected to localized impulse loading, but the transmitted forces must depend upon the thickness and strength of the faces which control the face stretching forces [1,2,8]

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