13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- There are many papers which deal with the geometries and the properties of auxetic materials, but there is little information on the behavior of the sandwich panels with chiral configured cores. In this paper, the meta-chiral structure with parallelogram-shaped nodes as in Fig. 3 will be analyzed separately, and as a core of a sandwich panel. Figure 1. Basic blocks for three chiral structures: a) trichirals, b) tetrachirals, c) hexachirals Figure 2. Structures from components of order 4: a) tetrachirals, b) anti-tetrachirals, c) meta-tetrachirals It is to note that in the analytical evaluations of auxetic in-plane properties of 2-D chiral, anti-chiral and meta-chiral structures, two different approaches were used: a) rigid ligaments and nodes, connected together through ideal hinges [2]; b) flexible ligaments connected with rigid or deformable nodes [9]. Also, it is possible to evaluate the out-of-plane mechanical properties of a chiral lattice analytically or by means of finite element analysis (FEA) [8,9]. 2. Geometry of the analyzed structure and the finite element model The behavior of the panel presented in Fig. 3 was evaluated by using a FEA model, with ANSYS [10]. The sandwich panel has sheets made from an aluminum alloy (1050 H24) of thickness tf = 1 mm, glued with araldite AW 106/HV953 U to the core made from rigid polyurethane strips having a section of 5 x 25.4 mm inside the panel and 10 x 25.4 mm on the border of the panel. The FEA makes possible the characterization of the sandwich panels under several aspects: rigidity, state of stress, fundamental eigenfrequencies and modes of vibration, stability. There were analyzed several cases of loading: 1) simply supported plate, loaded by a lateral pressure of 0.07 MPa; 2) cylindrical bending with the panel supported on two opposite edges and loaded by a lateral pressure of 0.05 MPa; 3) cylindrical bending with the panel supported on the other two opposite edges and loaded by the same lateral pressure of 0.05 MPa;
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