The primary purpose is to maintain a high moment

The use of composite sandwich structures in aerospace and
marine applications is increased 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). Also
sandwich materials are capable of absorbing large amounts of energy under
impact loads which results in high structural crashworthiness. A structural
sandwich is composed of two thin stiff face sheets and a thick lightweight core
bonded between them. A sandwich structure will give 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. Various combinations of core and face sheet materials are
utilized by researchers worldwide in order to achieve improved crashworthiness
In a sandwich structure, generally, the force couple formed by the face
sheets carry the bending loads and the lightweight core material carries the
shear loads. 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. Because of the  low density of the core material the panel
density will be low so that  under
flexural loading of  sandwich panels
there will be  high specific mechanical
properties relative to the monocoque structures. Hence, sandwich panels are
much more  efficient in carrying bending
loads. The face sheets act together to form a force couple, where one laminate
is under compression and the other under tension during flexural loading
and  the core of sandwich material  resists transverse forces and stabilizes the
laminates against global buckling and local buckling. They also yield an
increase in buckling and crippling resistance to shear panels and compression
members. In automotive industry the out of plane compressive properties are
more critical, whereas in wind turbines the in plane compressive properties are
more importance hence, the critical properties of sandwich composites vary
according to the application area of the structure. The objective of this study
is to understand the mechanical behaviour 
of multi layered sandwich structures with polyurethane core and glass
fibre face sheets fabricated by vacuum bag moulding technique. In this project,
flatwise compression (FC), edgewise compression (EC), Mode I inter laminar
fracture toughness and three point bending (3PB) tests were conducted on multi
layered sandwich specimen