the use of sandwich core
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.


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.


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 attack.



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.


The use of core decreases 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.


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.


A disturbing 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.

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.

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.
 
 

 

 
 

pricing, availability and specifications subject to change without notice