Is cork a bad sandwich material.

Ask silly questions then be prepaired for equally silly answers !

Its been a silly unthinking question and some one in another year or so will ask yet again CAN I USE CORK AS A CORE? and this will happen all over again !!

 

Structurally - no, there are better choices. Acoustically, perhaps

 

sound travels through hard materials cork soaked and buried in resin is hardly going to be a soft material any longer , so Acoustically , very doubtful!!
Sorry no mater what cork as a core in any shape or form is a no no !! so why bother !

 

How do you build a structural..Acoustic foam core panel ? Is there such a thing or is the acoustic material added to the panel skin ?

How do they build the engine room on a first class composite boat ? Sample Layup schedule for Acuostic and fire retardant ?

 

The foam sheet has a lead layer part way unto it and has a silver outside . comes i variable thickneses ,cost a small fortune ,and when done properly is really quiet .

AND NO LEAD SHEET IS NOT A CORE MATERIAL EITHER !! SO DONT EVEN THINK ABOUT IT !!

 

Must be more to it than that.

 

Maybe you should stick to expounding on Wheaties and peanuts, Tunnels, stuff you might actually know something about.

http://www.udel.edu/udaily/2012/jun/cork-sandwich-composites-061812.html

http://www.corecomposites.com/composites/core/cork/

http://www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/Cork-sandwich-construction/?page=2

http://dspace.mit.edu/handle/1721.1/68899

 

Interesting. Thanks for the link

 

i infused a few test pieces of corecork... the way it seems to work is that the resin fills the large voids in the corecork, which in turn forms a lattice of resin in between the cork cells. So the cork, is not really doing much except providing a low density space for the resin to form around. I think the lattice of resin adds significantly to the core properties, which cross links the laminate right through the core.

It does not have a valid application in a thick core. Other materials are more suitable where the core is required to be in excess of 6-10mm thickness. Where this stuff shines, is in thin core applications - such as those of the previous tetimonials of the 2mm veneer of stand up paddle boards, sailboards etc. In thin core applications, the additional weight is negigible as the cork itself doesnot absorb resin - only the voids between cells fill with resin. So if you infuse a 4-6mm thick corecork panel, it comes out the same weight as 80kg/m3 foam cored panel because the surface of the foam absorbs so much resin. The thin stuff is also drapable, so compound curved parts are simpler to setup as opposed to using other rigid core materials.

So yes it has a place, but large boats will not find much use for it. Heaps of the kayak and windsurfer guys are already using it, so for small boats i can see some good uses for it.

 

Again, it's a relatively low density core and even the Cork Core folks don't recommend it for infusion or highly loaded panels. It certainly has potential on many projects where 5 to 10 foam would normally be employed, but it's not particularly light, so what's the real gain. The whole point of a sandwich laminate is to save weight, for the same panel strength and stiffness. Cost is a mitigating factor often, so cork could make inroads into the industry.

 

http://corkcomposites.com/industry.php

We have used quite a bit of this material and it works very well. Infused and hand laid up. We've used it in water parks for platforms and decks that get knocked around quite a bit and they hold together OK. Peter

 

If the real advantage is the open spaces get filled with resin and provide the actual structural connection between the face sheets, could we take EPS punch holes thru it to make the same grid work of resin and benefit from the reduced density of EPS verses cork?

Should we make a slurry of epoxy, milled glass fibers, and microballons to fill the channels we made in the EPS so the grid work is lighter than solid resin.


Thanks for the links, I never would have believed any real value, Can't believe I would have sided with Tunnels on anything.

 

Forget about EPS and slurries, they will be heavier than commercially available cores. Firstly a core needs to have a high shear stress. Hard to beat balsa or honeycomb on that front. Then it has to be flexible. If the core is flexurally stiff and it attracts flexure stresses then it has to be strong enough for the flexure. Thats why cores have low bending stiffness so they do not have to be strong. They only transmit the shear strain from skin to skin. I've had clients mucked about for years trying to do better than commercial cores and they have failed. Just pick the core that does the job and try to beat down the suppliers cost as low as possible. Peter S

 

Peter is correct, if you make a grid of reinforced epoxy, the weight issue alone will discount any advantages. I'd like to see some independent testing and full up physical properties with different engineering approaches (laminate types, layups and resin systems, etc.).

 

Peteneng,

You are talking about a specialized low tech segment of the core industry.
To get minimum weight with maximum flexural strength/ stiffness of the sandwich, you need a stiff core in shear, otherwise the core moves, the skin moves, and you did not get the stiff overall panel. That is the reason eps is so bad, it has very low shear stiffness.
One of the greatest light weight cores is graphite ligaments at 45 degrees to the face, integrally adhesively bonded to graphite skins.

When we talk about boat type foam cores we are actually talking about relatively low performance core. Still works good since we are talking about relatively low performance structures.

I have tried multiple times to introduce a foam core to our (my company) aircraft structure, it always is higher weight, lower stiffness, and lower strength. Looses every time. I did get a full sized model made with foam once. The structure previously used was much worse than a boat hull.

Par,
With all due respect, have you ever examined fiberglass core? That is one form of reinforced epoxy. Not what I suggested above.

My point was that if the actual value of corkcore was to provide paths for epoxy to bridge the face sheets, we could find a way to make that a lot lighter. I don't think that theory is correct.

I agree with you about the independent testing, but what did you think about the links provided?