Issue 30

D. Tumino et alii, Frattura ed Integrità Strutturale, 30 (2014) 317-326; DOI: 10.3221/IGF-ESIS.30.39 324 Figure 7 : Determination of the torsional stiffness: loading scheme 1 (left), experimental setup (middle) and FEM model (right). Figure 8 : Loading scheme 2 to couple flexural stiffness in x and y (left) and loading scheme 3 to couple flexural and torsional stiffness (right). In particular, scheme 2 on the left of Fig. 8 couples terms D x and D y of the total stiffness matrix. The scheme 3 on the right, loaded in the centre and supported on two opposite vertex, couples flexural and torsional stiffness. This scheme can be considered as the superposition of scheme 1 (torsion dominated) and scheme 2 (x plus y flexion dominated), when the total load applied in scheme 1 is a half of the one applied to scheme 2. Panels have been tested and slopes of the load vs. displacement curves evaluated. Same loading schemes were applied to the FEM model in fig. 7 right and the slope of loading curves calculated. Results for loading scheme 2 are: 380 N/mm from experiments and 400 N/mm from numerical analysis. For loading scheme 3 are: 108 N/mm from experiments and 107.5 N/mm from numerical analysis. In TPB tests on x- and y- type beams, it was noted how transversal shear can play important role, especially when dealing with not particularly slender samples, as panels tested in this work. In numerical analyses performed to obtained results in sec. 3.2. and 3.3, to take into account of transversal shear deformation, a complete formulation of the shell element was used where terms D Qx and D Qy were added. This entities were calculated from TPB tests on the beams and reported in Tab. 3. C ONCLUSIONS he present work develops an analytical homogenisation model of the behaviour of a fully composite sandwich panel with a corrugated, trapezoidal shaped, core. The model is based on the reduction of the sandwich elementary cell unit, representative of the sandwich corrugation pattern, to a thick plate subject to small deformations, according to the approach proposed by Libove et al. [21,22]. An extension of the treatment in [21,22] is in particular proposed, able to consider the intrinsic ortotropy of the sandwich constituent elements, i.e. skin faces and corrugated laminate, when these are made of symmetric FRP laminates of equal thickness and lay-up. The present analysis has considered only the analytical evaluation of the flexural and torsional rigidities of the homogenised element, and the implementation of this formulation into a shell element of the ANSYS library. The compliance of the analytical homogenised model has been directly compared to the response obtained by a purely numerical three-dimensional model of the elementary sandwich cell. The values of the elastic constants obtained by the numerical simulation have resulted in good agreement with the analytical predictions. A number of experimental coupled and decoupled flexural and torsional tests have been performed on beam and panel sandwich elements, specifically designed in order to determine the experimental out-of-plane compliance response of the sandwich. All tests have indicated a significant influence of the transverse shear deformation component, indicating that the out-of-plane shear rigidity cannot be neglected. In the present work an experimental evaluation of the shear rigidity T