doi: 10.3850/S2010428611000109

On the Impact Behaviour of Sandwich Panels with Various Cellular Cores

H. Zhao¹, H. B. Zeng¹, I. Elnasri² and Y. L. Li^{3 1}Laboratoire de Mécanique et Technologie, ENS-Cachan/CNRS-UMR8535/ Université Paris 6, 61, avenue du président Wilson, 94235 Cachan cedex, France ²Laboratoire de Génie Mécanique, Ecole Nationale d’Ingénieurs de Monastir, Av. Ibn ElJazzar, Monastir-5019, Tunisie ³School of Aeronautics, Northwestern Polytechnical University, 710072 Xi’an, China

ABSTRACT

This paper reviewed an inversed perforation test on foam core sandwich panels under impact loading. The key point is the use of an instrumented Hopkinson pressure bar as a perforator and at the same time a measuring device. It aims at a high quality piercing force recordings during the whole perforation process, which is a weak point of common free-flying projectile – target testing schemes. Sandwich samples made of various cellular material cores (Cymat foam, Alporas foam, nickel hollow spheres, honeycombs) and 0.8mm thick 2024 T3 aluminium sheets as top and bottom skins are tested under quasi-static and impact loading. A significant enhancement under impact loading (20%) of the top skin peak load is found. In order to further understand this observed piercing force enhancement for sandwich panels made of rate insensitive materials, the sandwich with the cymat foam core and aluminium skin sheet is taken as an example. Using an elastic-plastic damageable model for the skin and an isotropic foam constitutive model for the core, a numerical model is proposed and validated. Virtual tests allow revealing that due to transient effects, the damage area in the skin sheet is larger under impact loading which leads to a larger deflection at breaking. The foam core is consequently further compressed and induces the piercing force enhancement of the top skin.

Keywords: Perforation, Sandwich panel, Cellular material, Impact, SHPB.

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