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Boria, Simonetta*, Forasassi, Giuseppe Department of Mechanical, Nuclear and Production Engineering, University of Pisa, Italy KEYWORDS – sandwich panel, crush behaviour, numerical simulation, LS-DYNA ABSTRACT – Aluminium sandwich construction has been recognized as a promising concept for structuraldesign of lightweight transportation systems. The aim of the present study is to investigate, experimentally and numerically, the energy absorbing capabilities of a thin-walled crash-box, made of aluminium sandwich material, for a racing car. The crash-tests were performed for a frontal impact at the velocity of 12 m/s; during the impact were measured the load-shortening diagram, the deceleration andthe energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, a series of strength tests were carried out on aluminium sandwich panel specimen to determine the material properties. INTRODUCTION For design and construction of lightweight transportation systems such as aircraft, high-speed trains,fast ferries and automobile, structural weight saving is one of the major considerations. To meet this requirement, sandwich construction is frequently used instead of increasing material thickness. This type of construction consists of two thin facing layers separated by a core material. Potential materials for sandwich facings are aluminium alloys or composites depending on the specific missionrequirement. Several types of core shapes and core material have been applied to the construction of sandwich structures. Among them, the honeycomb core that consists of very thin foils in the form of hexagonal cells perpendicular to the facings is the most popular. A sandwich construction provides excellent structural efficiency, i.e., with high ratio of strength to weight. Other advantages offeredby sandwich construction are elimination of welding, superior insulating qualities and design versatility. Even if the concept of sandwich construction is not very new, it has primarily been adopted for non-strength part of structures in the last decade. This is because there are a variety of problem areas to be overcome when the sandwich construction is applied to design of dynamically loadedstructures. The aim of the present study is to investigate the dynamic behaviour of a thin-walled crashbox for a racing car, built by Picchio S.p.A. and made of aluminium sandwich material (Fig.1).

Figure 1: Honeycomb sandwich structure.

In order to analyse its energy absorbing capabilities numerical simulations, with the explicit finite element code LS-DYNA (1), were used in addition todynamic testing. Different approaches for modelling sandwich structures by the FE method exist (2-4), which differ in modelling, computational cost and accuracy of the results and their adoption depends on the specific model size and loading case. A detailed representation of the hexagonal cells with shell elements (Fig. 2b) predicts well the cell wall deformation for impact simulations, but it isunsuitable for large scale models due to the computational cost and time required. A possible simplification may consist in representing the cellular core as an homogeneous continuum using the honeycomb structure’s effective orthotropic material properties (Fig. 2c).

Figure 2: Models for cellular core: a) real, b) detailed cell wall modelling, c) modelling with solid elements.

Since the maingoal of the presently discussed dynamic simulation of the crash-box is the consideration of the most part of the failure modes, a three-dimensional modelling approach with solid elements for the core and shell elements for the face sheets was adopted. STRENGTH TESTS OF ALUMINIUM HONEYCOMB SANDWICH PANELS Theoretically, a variety of possible failure modes for aluminium honeycomb sandwich panels can...
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