13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Performance of Sandwich Components with Chiral Topology Cores Marin Sandu1, Adriana Sandu1, Dan Mihai Constantinescu1,*, Ştefan Sorohan1, Dragoş Alexandru Apostol1 1 Department of Strength of Materials, University POLITEHNICA of Bucharest, Bucharest 060042, Romania * Corresponding author: dan.constantinescu@upb.ro Abstract Two thin plates with a stabilizing medium placed between them can be an ideal component for large and lightweight structures with increased strength, stiffness and stability. The application of the novel chiral cellular geometry will lead to the development of structural components with superior elastic and impact resilient properties. This paper proposes the design of lightweight square sandwich panels with aluminum sheets and a core made with a chiral geometry network having parallelogram-shaped nodes. Finite element analyses were undertaken in order to characterize the behavior of the considered panels as having supported edges, and loaded under lateral pressure. Also, the loading in torsion was analyzed in the case when two opposite corners are supported and in the other two corners equal and opposite normal forces are applied. For this loading experimental measurements were also done by using strain gages. The new meta-tetrachiral configurations under investigation can provide significant improvements in the mechanical performance of sandwich components, and may also be considered for advanced designs. Keywords Sandwich panel, Auxetic core, Meta-chiral topology, Finite element analysis, Strain gage 1. Introduction The strength and the stiffness properties of a sandwich panel are dependent to a great extent both on the behavior of the faces and of the structure used as core. Classical honeycomb core adopts a saddle shape (anticlastic curvature) upon out-of-plane bending, because its Poisson’s ratio is positive. In order to manufacture curved panels, cellular cores that exhibit auxetic properties (negative Poisson’s ratio) are used, because of their tendency to form dome-shaped surfaces. Consequently, curved sandwich panels with auxetic cores are basic components of advanced structures, first of all in the aircraft and automotive fabrication. It is evident that the analysis of the behavior of cores and sandwich panels under mechanical and thermal loading is of importance for designers. In paper [1], the finite element method has been applied to characterize the mechanical properties of re-entrant (auxetic) honeycombs which may be used as cores for sandwich panels with any special properties. In the last two decades, a number of cellular structures have been extensively analyzed [2]-[9]. Especially the periodic core structures with chiral topologies, which contain a number of interconnected basic blocks, have attracted considerable attention. A basic block is “chiral” if it is not super imposable on its mirror image. A basic block is consisting of a node with a number of 3, 4 or 6 ligaments attached to it (Fig. 1). Also, left handed or right handed blocks may be constructed. In the case of a chiral structure, the nodes are attached on the opposite sides of the same ligament (Fig. 2, a). It is possible to attach the nodes on the same side of each ligament and the corresponding structure will be denominated anti-chiral (Fig. 2, b). A hybrid construction, containing some nodes which are attached to the same side of the ligaments and some others to opposite sides of the ligaments, will be referred as meta-chiral (Fig. 2, c). In two-dimensions (2-D), the nodes may be circular, hexagonal, square, rectangular or with other geometry.
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