New Honeycomb Core

General Composites Discussions Composites Talk
#1

Aloha

My business partner and I are the inventors of a new type of honeycomb core which we see as having applications in the marine, aerospace, building, and other industries. You can visit our blog where you will find information to help you understand how it works, and how it differs, quite dramatically, from other cores in play today. http://honeycombcore.blogspot.com/

We recently discovered (within the last 2 months) that we can create the core quite easily using vacuum forming techniques, and feel that this might be the way to produce large sections of core inexpensively and to a high degree of accuracy and quality using materials selected especially for the usage required.

We would greatly appreciate your comments and suggestions as to how we should proceed from here.

Thank you

DJH

#2

I’d say give your product to a bunch of professionals and get hard results in a multitude of tests, including three point bending, impact, thermal stress etc. Engineers sure love numbers and if you can show favorable results you’d have an easier time selling your product.

On that note if you decide to hand out free samples sign me up, this core looks extremely interesting and it’d be cool to get a hands on look.

#3

Hi
Nice meeting you the other evening - sorry we couldn’t get together before you left. We want to manufacture some test samples of our core so we can get them tested as per your recommendation. What materials should we use, both for the core itself and the skins? I know this would probably be dictated by the end use, so choose materials that would be easily obtainable in Hawaii if possible!

thanks.

Check out Bob’s Picasa site - it has a whole bunch of stuff, a lot of which we would have shown you had we the time…

https://picasaweb.google.com/bobhexa

Aloha

David (See you next time you are in Hawaii!)

#4

Don’t worry about it. It was nice meeting you and hanging out at Hanks. You guys play good music!

For your core material you likely want to switch from this plastic to another material. Plastic is going to have bonding issues and currently your core is a bit weak and crushes easily. Which material though is a beast in and of itself but I would suggest Nomex since it’s already so widely used in composites. Not sure how Nomex processes but you definitely can’t vacuum form it.

Nonetheless this shape looks pretty neat, I’m curious to see how it fares over other cores.

#5

If a flight control were made of this core it would take years to water extract without an autoclave. That’s the only downside i see. One side is closed cell and the other is completely open.

#6

For applications where safety is the main issue but the weight is important:
High temperature distortion
Flame fast extinguishing and no smoke
High resistance to crushing loads
No retaining moisture
Low density
High shear strenght for structures designed for stiffness

About closed cells: as “clearly” explained by dallsab84 example I also suggest to consider only open cells for most advanced application. Although Nomex is used in flight controls or wing leading edges, the problem of moisture/humidity and temperature effects on air trapped in, always places problems when choosing this material (on a project I was explicitly requested by the customer to avoid the use of Nomex like cores)……although it is used in the end.
If used, as I’ve seen on some research product, one solution is to drill the faces of honeycomb in order to create a channel for air ; if your technology allows to implement this feature it would be interesting…
Closed cells with plastics could be interesting for infusion. Euro-Composites already patented its technology for such application.

#7

[FONT=Comic Sans MS]This was my very first attempt at venturing into the world of plastic vacuum forming. Whilst unable to acquire a supply of polystyrene on Hawaii, I was fortunate enough to discover a roll of shoji door material in the workshop. Not really sure what kind of plastic it is but it sure helped me to gain an idea of technique. The whole experiment is definitely a major success as it shows the potential for a fast, economic and high quality method of manufacture. There is a host of applications just waiting to be discovered to be added to the already recognized uses for this patented geometric matrix. Please check out my homemade vacuum forming jig.[/FONT]
[FONT=Comic Sans MS]https://picasaweb.google.com/bobhexa/HexaflexVacuumFolding#[/FONT]
[FONT=Comic Sans MS]I would love to be able to utilize Nomex but as you say it is not formable by vacuum method.
I am trusting that there is an appropriate plastic available. Perhaps because of the large surface areas available on this matrix for the attachment of laminar skins there should not be a bonding issue.
Materials of course depend upon final application.
This material could be an metal foil perhaps aluminum and formed by progressive folding techniques. However the vacuum forming method of manufacture is most preferable due to speed and economy.[/FONT]

#8

….Nomex is a fine material but use it to make standard honeycomb core and you will open up the possibility of delamination. As an ex aircraft engineer I totally understand the problems of closed cells which are the prime cause of delamination.
Perforated cores are standard avoidance techniques which could easily be incorporated into this core material. However the one side of closed cells that [COLOR=black][FONT=Calibri]Dallasb84 refers to are in fact filled with foam aluminum inserts which act as shear and compression components. All one needs is a pressure relief valve between core and ambient atmosphere and then there is no risk of high pressure build up within the core.[/FONT][/COLOR]
[FONT=Calibri]“Closed cells with plastics could be interesting for infusion.” Could you explain that further please?[/FONT]

#9

“Closed cells with plastics could be interesting for infusion. Euro-Composites already patented its technology for such application.”

Just checked this out …there is still the possibility of delamination of the barrier sheets from the closed core honeycomb.
Replace said honeycomb with this new matrix and “bingo!”…no more problems of delams.

#10

I totally agree Canyon that the matrix should be subjected to a full set of test procedures. I would like to compare the properties and attributes of this core material with standard aerospace honeycomb.
I wonder if I should make standard test specimen panels that are the same dimensions as what Hexcel specify for their testing specimens which apparently are the correct size to fit the testing equipment. Test specimens are normally prepared by bonding .032" AL 5052 thick facings to each side.
Is there another way I could demonstrate the attributes?
There is a technical problem: Hexaflex core being made from a single sheet has no need to be glued. It is not made by gluing ribbons together so there is no double wall thickness. The combined weight of the two shared walls in each hexagonal cell and the weight of the glue that is inherent in commercial honeycomb is sufficient to make a whole bunch of foam aluminum which is formed into hexagonal plugs that go into the hollows on the one side of this core material. To what benefit is this if the weight is the same as standard honeycomb?? Howabout the fact that this will never, and I repeat never, delaminate.
I mention this because the attributes of this core material will change according to how one shares out this saved weight. A higher density of foam metal in areas of higher stress and a lower density in low stress areas makes the testing procedures capable of variation!!
What do you guys think??”
:confused:

#11

Hi all,

Bobhexa, I supposed your last question is referred to my post, right ? If yes, here is my opinion.
I meant nomex like cores covered on both sides with thin “plastic” (i use a generic term) plies.
We know that if you infuse a sandwich panel where the core is nomex ( referred as a core with open cells), you face the problem of how to avoid to fill the cells with resin…at the end you can’t, unless there is some way to seal the cells in order to have only skins impregnated and not the cells full of resin.
One possibility is to place, between skins and core, a ply ( the plastic ply mentioned above ) which has two tasks:
[FONT=Calibri]- [/FONT]Seal the cell;
[FONT=Calibri]- [/FONT]Act as adhesive between core and skins.
In addition, for infusion, it could be necessary place holes ( as you find in some pvc core types for infusion) in order to have vertical flow of resin from one face of the core to the other, so that impregnation is uniform.
Such cores already exists, but they are currently made in thermoplastic material, then their mechanical properties are not so high if compared to nomex.
Years ago I read that Euro-Composites realized such products with nomex and I contacted them; unfortunately they don’t sell the products itself (that is nomex panels for infusion application), rather they “sell “ a patented technology ( in the same way of Scrimp,Vap or similar…) which deal with application of resin infusion for sandwich panels made with nomex cores.
Then back to my previous post: since ,with such cores, the two tasks above must be satisfied, I wondered if your techology was able produce them with the goal of infusion application. This question s not so trivial as it could appear,( I believe the “infusion community” can be happy ) since the aerospace sector is heavily searching realiable alternatives to autoclave technology and Liquid Composite Moulding is one of them. So, cores able to be part of these technologies could be welcomed.

#12

Aloha Wings ,
Thanks so much for all the very useful info you posted with regard to L.C.M.
I’ve been researching into this technology and see that this technique will certainly work with Hexaflex.
As I mentioned in my previous post to you the thin plastic plies or barrier sheets ( tech term) are more efficiently bonded to Hexaflex than to Nomex which will avoid any chance of delamination because the core of Hexaflex is ventable whilst Nomex is not and Hexaflex has a larger surface area to bond to the barrier sheets than Nomex has.
Nomex is made of ribbons glued together. Nomex transverse shear properties are dependent upon the direction of the ribbons. Hexaflex is not formed from ribbons glued together. The complications of transverse shear are not inherent in Hexaflex. The mechanical properties of Hexaflex will be higher than Nomex by virtue of the inserted hexagonal foam metal plugs which I have mentioned in my previous post.
Many thanks again Wings for your input.
Bobhexa

#13

You’re welcome…

One question: which minimum density do you plan to reach with this material ?

#14

Aloha Wings,
The density that I am planning to reach with this core material would be to equal what is considered the best and lightest honeycomb core material presently available on the market.
Hexaflex core material is structurally featherweight in comparison with commercially available honeycomb core with its ribbons and glue.
My aim is not to make a lighter material but to equal the weight of the state of the art. The weight saving of Hexaflex is used to make the hexagonal foam metal plugs which provide the compression and shear which will raise its weight back to the weight of the state of the art.
Consider this to be an adaptation of commercial honeycomb in order to provide a greater surface bonding area and ventability, both of which are absolutely crucial factors to prevent delamination.
An aircraft spends possibly 20% of its time out of service being expensively checked for delamination. In the old days we used to tap the skin with a threepenny bit coin as a way to detect delamination of the skin from the core material.
Electric lightning bolts and ingress of water is the formula for a gradual core shredding.
Best wishes
Bobhexa

#15

Old thread, but I just Stumbled onto your blogspot website. I thought it was hilarious :slight_smile: I’m thinking…waaaaait, I’ve seen this before!!!

#16

Tell me more Riff!

#17

Not much more to tell then RANDOMLLY StumbleUponing this product. I rarely find anything composite related in my Stumbles…But I knew I saw it somewhere here!

#18

Nice idea, but I think that under compresion vertical walls will buckle under smaller pressure than standard honeycomb core. Walls of vertical hexagonal on your design are not connected to each other. I made quick FEA buckling analysis for standard cell and your cell. Standard cell can withstand 1.64 times higher pressure load. Its calculated with 20mm cell size (circle diameter), 10mm height, 0.5mm wall thickness and aluminium material. Both ends are constrained same way like when they are bonded to composite skins.

Also, there will be lower shear strength of the core because of those connections missing.

Mike

#19

Aloha CarbonMike,
I appreciate the work you have put in. I made a passing mention of foam aluminum in post #8.
Because this core material is not made of ribbons there is no glue. Also, in the ribbon form of honeycomb, 2 of its 6 walls in each cell has double thickness walls. This is a huge weight saving.
The amount of weight saved is turned into foam aluminum plugs which are put into the concavities.

https://picasaweb.google.com/116301488865807915087/HexaflexPatentNumber7541085IssuedJune2nd2009#5348108403238326914

Best regards,
Bob

#20

Yes you are right with those double walls, but not 2 walls from 6 but only one. You dont count with other cells around.

Yes you save that little weight, but you have already lot of weight added with those top and bottom hexagons (cell ,covers,). On your design, every cell is closed from top or bottom, no cell is fully opened. Its like honecomb fully covered with sheet from one side. And thats a lot of added weight. But I must say you also save some weight because you have less vertical walls than honeycomb. I dont have time to calculate it, but for some ratios of cell size/core thickness you can have same or higher weight than standard honeycomb.

If you say that you add those foamed aluminium plugs, you will add more weight. Of couse it will be more crush and shear resistant, but it will be maybe twice as heavy than standard honeycomb or worse. If you think that those foamed aluminium plugs are so lightweight, you can make core only from those, applied with some sort of honeycomb tool. Actualy you can use standard honeycomb to hold those hexagon plugs in place while bonding to first skin. But it will be pain to place all of them manualy in place.

No offence :wink: