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DuPont granted Dream (10/6/06) usage rights of the chart near
the middle of this page. It illustrates the substantial gain
that can be obtained through the use of sandwich core. Dream
is the only company in the world with this type of in-house ability
and expertise. We specialize in the use of sandwich core and
specific carbon fibers. We have been supporting optics with carbon
fiber structures since Dream's inception in 2003. Dream's advanced
composite structures have been used to support numerous substrate
types and materials, from monolithic to cellular (lightweighted
optics) and ULE to borosilicates. |
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As you can see below, when the distance between skins is increased
to 4t, the stiffness increases by 37 times and the strength increases
by 9.2 times, yet weight is only increased by 6%. Dream routinely
produces sandwich cored composites
with 8-15+ t. |
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The inverse of this is to use a sandwich core to arrive at a
given stiffness. When compared to a metal counterpart of the
same stiffness, the carbon fiber skinned sandwich core part will
be exceptionally light. The other two main benefits of the advanced
composite parts are that their CTE (Coefficient of Thermal Expansion)
is extremely low (slightly positive, zero or negative, depending
on project requirements) and it is more impervious to corrosion
and chemical attach. |
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There are two main types of sandwich core material: honeycomb
and foam. Within each are variations, like "honeycombs"
that are actually triangular shapes, hexagonal shapes, etc..
Within each of the two main types of sandwich core is a myriad
of different raw materials they can be made from. This can be
anything from paper to Kevlar (Nomex
is an example) to plastics to carbon fiber to ceramics, etc. |
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The use of core lessons the number of layers of advanced composites
needed and therefore resin used. Resin is far heavier than advanced
fibers. Sandwich core parts are lighter for this reason as well. |
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The main disadvantage to using core is that it makes part design
and fabrication much more complex and difficult. Dream specializes
in the use of sandwich core and is intimately familiar with how
to deal with its unique design challenges. Both from a fabrication
standpoint and also from a design standpoint so the part truly
does outperform all other choices.
Most applications desire lower moments of inertia in order to
accelerate, slew and decelerate faster. A stiffer structure also
yields better pointing, tracking and optical quality because
the entire system is more rigid and moves less due to thermal
deltas. |
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A distrubing trend... Recently we have been seeing more and more
companies advertise that they are using "sandwich"
carbon fiber tubes. Yet these "sandwich" tubes are
nothing more than solid laminate carbon fiber, with no sandwich
core at all, and are comparatively thin-walled. |
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A solid laminate carbon fiber tube requires a much greater number
of layers of carbon fiber in order to achieve the same stiffness
as the thick-walled sandwich
core tubes that Dream produces. This makes solid laminate
tubes, if they are the same stiffness, far heavier than what
Dream produces with carbon fiber skinned sandwich core. The numbers
listed on this page illustrate this characteristic quite dramatically. |
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As with so many other things in life, you get what you pay for... The
important thing is to educate yourself and know what it is your
are purchasing. |
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