Keywords: post-buckling, shear, multi-hinged rig.

Numerical and experimental approaches are needed to accurately measure and predict the response of thin aluminium panels under buckling and post-buckling conditions. Many papers [1,2,3] are concerned with metallic and composite laminate panels subjected to shear boundary conditions and are directed towards the assessment of the post buckling collapse strength of aeronautical panels. The simplest shear panel test equipment from the literature [4,5] is the picture frame: a square specimen is assembled with four rigid side members, which are pin jointed at their ends. The main disadvantage of classical picture frames for panel post-buckling analysis is the lack of the pure shear load condition induced by the excessive stiffness introduced by the frame at specimen boundaries. To overcome this disadvantage, in this work, a modified multi-hinged picture frame is used.

The paper investigates the behaviour of an aluminium alloy shear panel both in experimental and numerical ways. The experimental activity is performed using an in house designed and realized prototype of a servo-hydraulic multiaxial testing machine [6] equipped with an in house made multi-hinged square test rig, capable of imposing a pure shear mode load, and a strain gauge and laser meter data acquisition system. The specimens, made of Al 6082 T6 sheet with a thickness of 1 mm, are tested under pure shear load boundary conditions up to buckling and post-buckling occurrence. Finite element results are obtained using the nonlinear large deflection capability of the ANSYS code, considering geometric and material nonlinearity and friction effects into the hinges. The results are compared with the experimental ones. More precisely, the comparison of numerical and experimental out of plane displacements shows a satisfactory agreement. In the same way a good correspondence is obtained with the comparison of the out of plane displacement versus longitudinal displacement plots.

1

C. Calì, E. Armentani, F. Caputo jr., G. Godono, "Macchina per prove di pannellature aeronautiche sotto carichi multi assiali", Proceedings of XXVIII AIAS, Vicenza, 1999.

2

A. Apicella, E. Armentani, C. Calì, F. Caputo jr., R. Esposito, "Buckling and post-buckling analyses of a GLARE thick flat side panel", Proceedings of ETCE/OMAE2000 Joint Conference, New Orleans, 2000.

3

C. Calì, E. Armentani, F. Caputo jr., G. Cricrì, R. Esposito, "Numerical solution techniques for structural instability problems", Journal of Achievements in Materials and Manufacturing Engineering, 19(1), 53-64, 2006.

4

T.C. Wittenberg, T.J. van Baten, A. de Boer, "Design of fiber metal laminate shear panels for ultra-high capacity aircraft", Aircraft Design, 4, 99-113, 2001. doi:10.1016/S1369-8869(01)00003-9

5

S.J. Guo, "Stress concentration and buckling behaviour of shear loaded composite panels with reinforced cutouts", Composite Structures, 80, 1-9, 2007. doi:10.1016/j.compstruct.2006.02.034

6

C. Calì, M. Perrella, "Design of a prototype of servo hydraulic multiaxial testing machine for specimens, structural elements and structures", Proceedings of ICAD2006, Firenze, 2006.

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