Download Sandwich Materials

SANDWICH CONSTRUCTION
PRINCIPLES OF SANDWICH CONSTRUCTION
1. Two facings, which are relatively thin and of high strength,
1. a core is enclosed which is relatively thick and light and which has adequate
stiffness in a direction normal to the faces of the panel.
Many alternative forms of sandwich construction may be obtained by combining
different facing and core materials.
The facings may be steel, aluminium, wood, fibre-reinforced plastic or even
concrete.
The core may be made of cork, balsa wood, rubber, solid plastic material
(polyethylene), rigid foam material (polyurethane, polystyrene, phenolic foam),
mineral wool slabs or from honeycombs of metal or even paper.
a) panel with a polyurethane or polystyrene core
b) panel with a metal or paper honeycomb core
c) panel with a mineral wool core
For a symmetric sandwich section with a low modulus core, the bending stiffness
and the bending stiffness-to-weight rato are given by
where, Es = modulus of the skin material,
Ρs = density of the skin material,
b = width of the section,
t = thickness of the skins and
d = distance between the skins.
Steel–polymer–steel and
aluminum–polymer–aluminum are
two commercially available sandwich
materials developed for body
structures as well as for body panels.
Sandwich panels with carbon fiber reinforced polymer in the skins and a polymer
foam core can provide much higher weight saving opportunity for body
applications.
SANDWICH MATERIALS
•vibration damping group
•lightweight construction
The inner and outer skins typically consist of five or seven layers of
various material thickness and type, dependent on the specific
strength required at different locations, and optimized by finite
element analysis.
The actual form of the body panel material is essentially a sandwich
of aluminium honeycomb between layers of multi-ply carbon fibre
reinforced resin.
SEQUENTIAL CO-INJECTION OR SANDWICH MOLDING
Each of the five parts comprises a rigid polyurethane foam core of 110 kg/m3 density. Glass-fibre
mat is preformed and wrapped around the foam core before being placed into the low pressure
injection tool. To ensure accurate location, the glass mat is retained in the part line of the tool.
Polyester resin is then injected into the tool which impregnates the glass fiber and completes the
sandwich construction.
ADVANTAGES
•lightweight nature of the thermoplastic core
•stiffness,
• corrosion resistance
•surface appearance of the metallic outer layers.
DISADVANTAGES
•this material type is only viable for components that are assembled
into the body after the painting process
•this material is not weldable and must be assembled by a cold
joining process of either adhesive bonding or mechanical fastening.