FEATURE Honeycomb core
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For years, PET (polyethylene terephthalate) foam has been the
most common core material used by builders, but now it is facing
increasingly competition from the latest generation of honeycombs
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Core comparison
Relative stiffness
Thickness
1T 2T 4T
Stiffness 1737
Weight 1 1.05 1.10
Kevlar
Nomex
Balsa
Cost $ Foam
Aluminium
PP Honeycomb
Weight lb/ft3
ABOVE Resin being applied to a core in the traditional way. However, honeycomb’s structure makes it ideal
for infusion and other closed mould processes
t’s well-known that sandwich Honeycomb, on the other hand is that the manufacturing process must I
construction offers superior intrinsically superior in dealing with be more expensive than foam. And a
strength-to-weight performance shear (along the skin surface) and moment’s thought reveals the secret of
than solid laminate when it comes compressive loads. its lightness — around 95 per cent of a
to specific stiffness. However, for One way to look at a honeycomb honeycomb structure is air!
optimised results and cost effectiveness, core and its inner and outer skins is as
the core and the inner and outer skins an almost infinite number of I-beams 1=AB03<347B
must be designed to work as a package — called girders when used in the But manufacturers are saying that
and complement each others’ virtues. construction industry. The skins are the thanks to new, more cost-effective
Getting the core material right is flat top and bottom sections, while the manufacturing techniques honeycomb
therefore a matter of intense interest core is the vertical web holding them now offers improved performance and
to all those who build in GRP or other apart. Stiffness depends very largely on cost advantages.
composite materials. the depth of the web. Honeycomb comes in many
Polyethylene foam is an inexpensive But unlike a girder, which provides different varieties. Due to its ease of
and effective core material that has stiffness only in the plane of the web, use, the most popular for production
served the boating industry well for honeycomb has webs running in many boatbuilding is PP (Polypropylene).
several decades. One of its advantages directions and is therefore equally stiff Stepping up from this in performance
is that it’s a relatively homogenous in all planes. and price, is Nomex, Kevlar and
material that clearly offers a large Honeycomb has long been aluminium – although the last is
bonding area to the inner and outer recognized as a high performance core normally used only with carbon/epoxy
skins. But from a purely engineering material (one reason for its universal skins for top competition racing yachts.
point of view its non-dimensional popularity in the aviation industry) Kevlar is used for the latest generation
aspect makes it less than ideal. but one look at its structure tells you of high performance honeycomb cores,
" August/September u0s www.europeanboatbuilder.net
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