The under impact loads which results in high

The use of
composite sandwich structures in aerospace and civil infrastructure
applications has been increasing especially due to their extremely low weight
that leads to reduction in the total weight and fuel consumption, high flexural
and transverse shear stiffness, and corrosion resistance (ASM Handbook 1987).
In addition, these materials are capable of absorbing large amounts of energy
under impact loads which results in high structural crashworthiness. In its
simplest form a structural sandwich, which is a special form of laminated
composites, is composed of two thin stiff face sheets and a thick lightweight
core bonded between them. A sandwich structure will offer different mechanical
properties with the use of different types of materials because the overall
performance of sandwich structures depends on the properties of the
constituents (Daniel 2008). Hence, optimum material choice is often obtained
according to the design needs (Vinson 1999). Various combinations of core and
face sheet materials are utilized by researchers worldwide in order to achieve
improved crashworthiness (Adams 2006). In a sandwich structure, generally the
bending loads are carried by the force couple formed by the face sheets and the
shear loads are carried by the lightweight core material (Nguyen, et al. 2005).
The face sheets are strong and stiff in both tension and compression as
compared to the low-density core material whose primary purpose is to maintain
a high moment of inertia. The low density of the core material results in low
panel density; therefore under flexural loading sandwich panels have high
specific mechanical properties relative to the monocoque structures. Therefore,
sandwich panels are highly efficient in carrying bending loads. Under flexural
loading, face sheets act together to form a force couple, where one laminate is
under compression and the other under tension. On the other hand, the core
resists transverse forces and stabilizes the laminates against global buckling
and local buckling (Glenn and Hyer 2005). Additionally, they provide increased
buckling and crippling resistance to shear panels and compression members. The
critical properties of sandwich structures vary according to the application
area of the structure. In automotive industry the out of plane compressive
properties are more critical, whereas in wind turbines the in plane compressive
properties are more important.. The objectives of this study is to understand
the mechanical behaviour and failure mechanisms of multi layered sandwich
structures with polyurethane core and glass fibre reinforced polymer (GFRP)
face sheets fabricated by vacuum bag moulding technique. For this purpose, flat
wise compression (FC), edgewise compression (EC), Mode I inter laminar fracture
toughness and three point bending (3PB) tests were conducted on multi layered sandwich
specimens.