Introducing novel sandwich panels based on of cork/polyurethane foam hybrid core and composite grid structure for marine applications

Low-density polyurethane foams as the low-cost and lightweight materials are used to produce some structural parts of marine vessels. However, these foams have low mechanical properties and they are susceptible to water and moisture penetration. The presence of initial defects or impact-induced damages on the external surface of the marine vessels can lead to the water penetration into the foam core, which generally results in core decay and, subsequently, delamination in core/skin interfacial bonding. Thus, the main objective of this research is to reduce the weaknesses of low-density polyurethane foam-based structures by introducing a novel material in this field. For this purpose, a sandwich panel with a hybrid core consisting of agglomerated cork and low-density polyurethane foam reinforced by a composite grid from epoxy/glass fibers structure is successfully designed, fabricated, and tested. Results of 100-days aging indicated that the water absorption of novel specimens was less than half of the conventional polyurethane-based specimens. In addition, replacing the stiffened cork/polyurethane hybrid core instead of the polyurethane core resulted in 506, 814 and 144.94 % increase in maximum flexural load, initial flexural stiffness and flexural toughness, respectively. In the following, the structural behavior of both the novel and conventional structures was investigated by numerical simulation of bending test. The results of numerical analysis showed that the flexural stiffness of novel panel was enhanced about 884%, comparing to the conventional structure.