The use ofcomposite sandwich structures in aerospace and civil infrastructureapplications has been increasing especially due to their extremely low weightthat leads to reduction in the total weight and fuel consumption, high flexuraland transverse shear stiffness, and corrosion resistance (ASM Handbook 1987).In addition, these materials are capable of absorbing large amounts of energyunder impact loads which results in high structural crashworthiness. In itssimplest form a structural sandwich, which is a special form of laminatedcomposites, is composed of two thin stiff face sheets and a thick lightweightcore bonded between them. A sandwich structure will offer different mechanicalproperties with the use of different types of materials because the overallperformance of sandwich structures depends on the properties of theconstituents (Daniel 2008). Hence, optimum material choice is often obtainedaccording to the design needs (Vinson 1999).
Various combinations of core andface sheet materials are utilized by researchers worldwide in order to achieveimproved crashworthiness (Adams 2006). In a sandwich structure, generally thebending loads are carried by the force couple formed by the face sheets and theshear loads are carried by the lightweight core material (Nguyen, et al. 2005).The face sheets are strong and stiff in both tension and compression ascompared to the low-density core material whose primary purpose is to maintaina high moment of inertia. The low density of the core material results in lowpanel density; therefore under flexural loading sandwich panels have highspecific mechanical properties relative to the monocoque structures. Therefore,sandwich panels are highly efficient in carrying bending loads.
Under flexuralloading, face sheets act together to form a force couple, where one laminate isunder compression and the other under tension. On the other hand, the coreresists transverse forces and stabilizes the laminates against global bucklingand local buckling (Glenn and Hyer 2005). Additionally, they provide increasedbuckling and crippling resistance to shear panels and compression members. Thecritical properties of sandwich structures vary according to the applicationarea of the structure. In automotive industry the out of plane compressiveproperties are more critical, whereas in wind turbines the in plane compressiveproperties are more important.
. The objectives of this study is to understandthe mechanical behaviour and failure mechanisms of multi layered sandwichstructures with polyurethane core and glass fibre reinforced polymer (GFRP)face sheets fabricated by vacuum bag moulding technique. For this purpose, flatwise compression (FC), edgewise compression (EC), Mode I inter laminar fracturetoughness and three point bending (3PB) tests were conducted on multi layered sandwichspecimens.