13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 4) torsion of the panel by applying two equal forces in opposite corners and restricting the movement of the other two corners [11]. In the numerical model the adhesive was considered only in between the upper and lower aluminum sheets and the chiral core which presumably behaves as a monobloc structural component, although the core was built as a “puzzle” from separate parts glued between them. For the used materials the following material parameters were adopted: aluminum – E = 69000 MPa, ν = 0.33, σu = 138 MPa (ultimate strength), σy 0.2 = 132 MPa (0.2% offset yield limit), density 2700 kg/m3; araldite AW 106 – Ea = 1350 MPa, νa = 0.45, σua = 33 MPa, τua = 23 MPa, density 1500 kg/m3; rigid polyurethane foam – Ef = 220 MPa, νf = 0.3 , density 301 kg/m3. The allowable stresses will be considered as 100 MPa in aluminum, 5 MPa in the polyurethane foam and 20 MPa in the adhesive. The dimensions of the panel are: a = 400 mm, b = 48 mm, c = 32 mm, tf = 1 mm (thickness of the sheets), ta = 0.3 mm (thickness of the adhesive), tc = 25.4 mm (thickness of the core), ts = 5 mm (thickness of the strips used to built the core), tb = 10 mm (thickness of the border). Figure 3. Geometry of the analyzed panel In generating the chiral network (Fig. 4) was used the basic block obtained by adding to the configuration from Fig. 5 its own image in mirror. The FE mesh is done by using solid 8-noded elements (Brick 8), and resulted as having 134728 elements and 185706 nodes. Two layers of elements were used over the thickness of the strips which form the chiral core and through the thickness of the sheets, and one layer of elements through the thickness of the adhesive. After a preliminary study it was established that a geometrically nonlinear analysis (large displacements) doesn’t lead to results clearly different from the ones obtained in a small
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