Multiscale approach for the design of composite sandwich structures for train application A. Zinno * , E. Fusco, A. Prota, G. Manfredi Department of Structural Engineering, University of Napoli Federico II, Via Claudio 21, 80125 Napoli, Italy article info Article history: Available online 1 September 2009 Keywords: Sandwich structures Railway vehicle Mechanical characterization Adhesive joints abstract In the present work a multiscale approach is considered for the design of composite sandwich structures for a roof of railway vehicle. The procedure consists in different steps that start from cost/benefit analysis on materials and their manufacturing process and cycle up to analysis of sub-components and entire structures. Each step is characterized by experimental, theoretical and numerical studies. The design activities herein presented count experimental campaigns able to characterize both the properties of novel sandwich material, manufactured expressly for transportation industry, the sandwich and joint behaviors. Analytical and numerical approaches have been used to validate and optimize the structural layout. Finite element analysis has been also performed on a test article to verify the ‘‘new” sandwich roof in regard to structural requirements suggested by European Code. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Sandwich composite structures consist of two thin, stiff and strong fiber reinforced composite face sheets (skins) separated by a thick layer of low density material (core) which may be much less stiff and strong. The role of the face sheets, due to the higher elastic properties, is to withstand bending and in-plane actions, while the transverse shear loads are sustained by the core. The bending stiffness of this type of structural arrangement is much larger than that of a single solid plate of same total weight made of the same materials as the faces. For this reason, composite sandwich structures are widely used in high-perfor- mance applications where weight must be kept to a minimum, for example aerospace structures, high-speed marine craft and trains, and racing cars. Common materials for the sandwich skins are composite or wood laminates and thin aluminum sheets. Polymeric expanded foams are frequently used for the core which, for more demanding applications, can alternatively be made of aluminum or aramid composite honeycomb. It is quite difficult or impossible to gener- ally define the best combination of sandwich constituents because the choice of materials depends not only on strength and stiffness requirements but also on process and cost considerations. More- over, other interesting properties of the constituents can influence the design choices, such as fire and environmental resistance, ther- mal and acoustic insulation, vibration damping and damage tolerance. The peculiar morphology of a sandwich panel—the layered and multimaterial structure—requires special attention during the design phase. Reliable stiffness and strength predictions can be made only by using suitable, accurate methodologies accounting for the intrinsic structural complexity and the several failure modes that a panel can experience. The theoretical anal- ysis of sandwich panels is summarized by Allen [1] and more recently by Zenkert [2] and Vinson [3], including a systematic design strategy for stiffness and strength. It has been recognized that sandwich beams could fail by a number of competing mech- anisms. Numerous investigators [4–6] have used the ‘‘failure mode map” concept for sandwich beams in bending to show the dependence of failure mode upon the geometry and the rel- ative strength of both skins and core. The concept of failure mode map is extended to give a useful design tools for sandwich structures that can be optimized by minimizing an objective function such as weight or cost against a set of constraints such as structural stiffness or strength. Frosting and Baruch [7–9] used variational principles to develop a high-order sandwich panel theory, which includes the transverse flexibility of the core that is capable to model the local effects at the load points. ‘High-order’ refers to the non-linear way in which the in-plane and vertical displacements are allowed to vary through the height of the core, in contrast to simple beam theory where the core in-plane displacements are assumed to vary in a linear way through the depth, and the out-of-plane displacements are assumed to be constant. Recently sandwich structures are investigated for structural ele- ment of railway vehicle body. Belingardi et al. [10] analyze glass fiber composite–foam sandwich structures for the structural 0263-8223/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2009.08.044 * Corresponding author. Tel.: +39 0817686336. E-mail address: alberto.zinno@unina.it (A. Zinno). Composite Structures 92 (2010) 2208–2219 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct