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In this paper, various sandwich panels with different face-sheet materials and three types of aluminum honeycomb cores are fabricated, the covers are made of either aluminum or glass fiber reinforced epoxy, and the panel's quasi-static behavior was examined using three tests; flexural, edgewise, and flatwise. The cores used in the panels have different properties according to cell sizes and heights. All manufactured panels have the same thickness. The results were presented as curves and tables so that the variables influencing the panel's durability could be determined. Results showed that flatwise compressive strength increased for specimens using covers made of aluminum material than fiberglass by about 40%. Samples that employed cores with smaller cell sizes showed more compressive strength in the flatwise direction than specimens using larger cells of cores by about 15%. While compressive strength in a direction that is parallel to the face sheet showed higher values for specimens of a fiberglass cover than aluminum material covers by about 14%. Flexural strength has decreased by samples using covers made of fiberglass than aluminum material by about (40 -- 90) % depending on the face-sheet thickness and cell size. Specimens with epoxy-filled cores showed the maximum compressive strength values in all cases. During flexural and edgewise tests, de-bonding failure has occurred commonly in samples using aluminum skins. [ABSTRACT FROM AUTHOR]

This paper aims to study the dynamic behaviors of particular sandwich panels manufactured using three specifications of aluminum honeycomb core with fiberglass or aluminum face-sheet materials. Three groups of panels were designed and manufactured, each including three different sorts of samples, all fabricated with the same thickness. A cantilever fatigue test was conducted on specimens, and the results were collected and presented in curves to detect the factors that affect the panel's endurance. The finding showed that the specimens with aluminum skin had more probability of face-sheet/core delamination. Samples of fiberglass covers showed face-sheets cracks or cores cracks more than delamination failure, while samples of epoxy-filled cores experienced the specimen’s global crack. Generally, specimens with aluminum covers and epoxy-filled cores resisted fatigue load more than other specimens. The larger honeycomb cell-size specimens showed more probability to face-sheet/core delamination failures than samples with smaller cell-size cores.

The buckling and postbuckling behavior of thin toroidal shell segments composed of auxetic core and graphene-reinforced face sheets under radial loads is reported in the present research combining exiting analytical solutions with the new material designs. Three types of graphene distribution of laminated face sheets and the lattice auxetic core are considered for convex, concave toroidal shell segments and cylindrical shells. The honeycomb lattice auxetic core can be modeled applying a homogenization technique. The Stein and McElman approximation can be used for longitudinally shallow shells to establish the nonlinear equilibrium equations in the framework of the Donnell shell theory with geometrically nonlinearities taking into account the two-parameter foundation model. The expressions of the radial load-maximal deflection postbuckling curves are achieved using the Galerkin method. The numerical investigations indicate the remarkably positive effects of honeycomb auxetic core and graphene-reinforced face sheets on nonlinear buckling responses of shells. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to provide an analytical approach for the nonlinear buckling behaviors of toroidal shell segments made by three layers included honeycomb auxetic-core and two Graphene reinforced face sheets under axial compressive or tensile loads. The auxetic core is designed in a honeycomb form and three distribution laws of Graphene are considered for two symmetric face sheets. The homogenization technique for honeycomb auxetic plates and shells is applied to establish the stiffness formulations of the core. By approximating the doubly curved coordinate to the simpler coordinate with the Stein and McElman assumption, the nonlinear basic equations are formulated using the nonlinear Donnell shell theory and the model of the two-parameter foundation. The Galerkin method can be performed three times for three states of buckling responses and the expressions of the load-deflection postbuckling curves can be determined. The numerical examinations present that the bifurcation buckling occurs with both axial tensile and compressive loads for convex and concave shells and the significantly beneficial effects of auxetic core and functionally graded Graphene reinforced face sheets on nonlinear buckling responses of shell segments. [ABSTRACT FROM AUTHOR]