Hybrid laminates. 1

[RPstress]

Does anyone have experience of hybrid laminates (e.g., carbon and glass or carbon and Kevlar)?

We're doing very preliminary design for a bird strike resistant aircraft structure, and would like to get a feel for a starting point.

Although the bird will dominate the design, we're interested in basic hybrid properties as well as impact, as the part will still have to function as a structure.

We know of a carbon-glass hybrid that we're sure is good at taking load after severe damage, but we're vaguer when it comes to a hybrid that resists damage to start with. Previous work has shown that carbon alone won't be weight efficient.

 

[Compositepro]

Kevlar will certainly be the toughest material to prevent penetration after failure but it will significantly degrade the properties on a carbon laminate and cause it to start fracture at a lower load than pure carbon. Kevlar has a negative axial CTE like carbon but the radial CTE is twice that of epoxy. This leads to micro-cracking in laminates and wicking of moisture. S-2 glass hybridizes much better. A better approach might be to use a Kevlar spall liner behind the carbon structure. Having the Kevlar as a separate layer may make it more effective.

 

[RPstress]

Thanks for the thoughts.-R.

 

[allcomposites]

We have study an application with hybrid fabrics and came up with the conclusion that AS4/S2 performed better than AS4/Kevlar. Our observations are well explained in the post of Compsitepro. Kevlar use is also limited due to hygrothermal effects.
I heard that carbon/polyethylene hybrid laminates are much better than carbon/glass, but never used Dyneema.

 

[RPstress]

Interesting.

We've thought quite hard about Dyneema/Spectra and the main drawback we see is that it limits the maximum processing temperature (the low compression properties also have to be kept an eye on).

The Dyneema people thought it might survive a 250°F/120°C cure, but they weren't certain of the fibre properties afterwards (it melts at about 150°C). They thought a 10%–30%/90%–70% Dyneema/carbon blend would be worth looking at.

 

[PanelGuy]

Pretty much everything I have ever seen so far is summed up here as far as hybrid weaves. Most everyone in the research has gone to distinct layers because of the factors above. Find the schedule for the Stryker armor plates, same deal. But it looks cool in commercial sporting goods...LOL

On the flip side...consider a different matrix. There has been a lot of work done in the thermal fusing of glass and Polyethylene for economy, but what about using a little higher temp TP. It would preserve the integrity of either the Carbon or Kevlar (seal the Kevlar too). Yes, you give up some laminate stiffness, but we are talking about being able to use geometric stiffeners right? I do not recall whom, but I did see a PEEK/Carbon in a medical application a few years back.

I would also consider the use of a Browning logo...it always seems to make the birds fly the other way very fast...

 

[RPstress]

Having looked Browning up I can see why. Expect to see the buck logo on leading edges across the world real soon now...

TP LE are being done by Stork Fokker in PPS on A340 and A380. About three years ago they had their doubts about manufacturing in PEEK (basically just the high temperature) and were looking at PEKK, though Victrex have their own doubts about PEKK (variable crystallinity issues) and prefer PEK, though that shares PEEK's high processing temperature.

The issue of whether to try a hybrid weave vs. hybrid laminate with separate plies of different materials is one that's been vexing us.

It's more doable with separate plies but intuitively it feels like separate plies might sacrifice some of the benefit. You might wind up with the worst of both worlds, rather than synergy.

I can't find any details about the Stryker armor. You say it had separate plies in different materials?

Most vests and the like seem to have one material to do the work, unless they're resistant to high velocity rounds and have a ceramic strike plate.

 

[PanelGuy]

The armor plating that I saw demo'd was multiple plies. I can imagine it is not readily findable. I seen to recall...there was a glas laminate external...general wear, a rubber ply to absorb differences, a thick ceramic plate to absorb loads, a carbon layer for stiffening and a glass backer to protect the interior...something like that any way. Much like a lot of armor lately has a steel backing plate with a kevlar or ceramic (or both) plate and then and offset thin steel to act as a spall liner.

BOdy armor is a whole different deal due to the need to be super flexible and having something (flesh) to stop the motion and absorb the energy...ouchy.

There was a ton of TP/woven roving at the ACMA show this year that was demonsrated as ballistic panels, I think Kazak took the award on it.

I always considered the Spectra and Kevlar to act like a catchers mitt and decelerate. It is why the Mongols wore solf sirts under their mail...same fiber reaction.

Ceramic has the mass to absorb the energy, but ultimately becomes ablative when it crushes.

Personally I would think there could be a great dynamic in a flexible matrix with a stiff fiber. It may be that a hybrid weave in a TP system would be the cats meow. Stiffening with the penetration resistance but still allow the matrix to lat the laminate flex without cracking. Probably really need to review the fiber sizing...LOL

Perhaps an energy absorbing backer? Consider that if you mount a piece of glass on a panel made of paper honeycomb and HPL backer that you can smack it on a table corner all day and not crack it. Dunno, I have not the background in bird strike energies. Anywhoo...my last two cents. That armor was developed in conjunction with U Del CCM and Anholt technologies, but it was like 15 years back.

 

[RPstress]

Was that this KaZak:

http://kazakcomposites.com/about-kazak-composites.html

?

They do seem to use multiple materials.

Thanks.

 

[Gunner]

You may want to think out of the box. Many thermoplastic resins offer great visco elastic properties and can be very tough. I would consider a Nylon 66 on carbon or glass. A hybird fabric could also be developed using the glass and carbon. The molding temperture would be 200F less than PEEK.

 

[rodneybennet]

Nylon 66 may swell too much (of course depending on the conditions). My experience is that currently used carbon and glass fibres do not restrain the swelling loads. Although nano particles could restrain in certain conditions (see

http://www.composite-agency.com/materials-forum.htm),

but this may be a bridge to far.

Cheers,
Rodney

 

[Gunner]

To Rodney
I have not experianced swelling with any nylon matrix. I have used N11, N12, N6, N66, N6/10 many time in the last 19 years plus in continious fiber composites. In a composite there is usally less than 50% by volume resin and it is less of a factor. I am developing a new prepreg process which will incorporate nano materials. See some parts at

http://www.amtxx.com.

Thanks,
Bob