The flexural and transverse shear stiffness, and

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.

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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 specimens