An analytical and experimental comparison of orthotropic sandwich panels using the Hydromat Test System

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A new two-dimensional test system, called the Hydromat Test System, simulates the hydrostatic and hydrodynamic loading conditions which are often present in actual sandwich structures, such as marine hulls. The test fixture uses a square 24 inch × 24 inch panel sample which is simply supported all around and has a distributed load provided by a water-filled bladder. In this study, the Hydromat Test System has been used to obtain data on sandwich panels with orthotropic face sheets and isotropic cores. This data has been compared to analytical expressions for the deflection and the in-plane strains based on small deflection sandwich panel theory. The engineering constants needed for the analytical solution were obtained from characterization tests of the face sheet materials. Core shear properties were obtained experimentally using two different ASTM standards. Four panels, with two different core materials and two different face sheets, were tested. Face sheet properties varied from slightly orthotropic (plane weave) to highly orthotropic (unidirectional), with an axial to transverse tensile moduli ratio of 1.2 and 3.9, respectively. The cores were closed cell foams with both a low and a high shear stiffness. The analytically obtained center panel deflection varied from 1 to 10% of that obtained by experiment. Most of the analytical tensile strains were less than 10% different from the measured ones. Both experimental deflection and strain data are in excellent agreement with the small deflection theory. It was concluded that the Hydromat Test System provides predictable and repeatable boundary conditions and loading mechanism and is a suitable method for testing soft cored, highly orthotropic sandwich panels. © 1998 Published by Elsevier Science Ltd. All rights reserved.

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Composites Part B: Engineering