spectra vs kevlar?

[sigurd]

hello,

Kevlar is sometimes used in the outer laminate of a cored hull, right next to the core, for impact protection.
At least for carbon outer layer, I guess that the kevlar will do nothing until the carbon is already broken. Right?

I have seen a few impact tests for spectra and kevlar (unfortunately only ballistic speed - not sure if low speed impact calls for different laminate attributes) - spectra does a lot better, and is lighter too. It is stiffer than kevlar, which leads me to think that it could take a much larger amount of load before the outer carbon or glass layer is broken. Am I thinking right?

Are there other caveats? For this application, which is preferrable, spectra or kevlar?

[robherc]

I'm not much of an expert on spectra, so I really can't compare the two that well, but isn't spectra FAR more expensive than kevlar? If cost is no object, and the spectra has higher ballistics ratings, and is stiffer, then my (semi-educated) guess would be that yes, the spectra would benefit your CF layup more...but I really don't know any more about spectra than that it's better than kevlar in ballistic vests.

[sigurd]

not much more expensive. about 10-12 dollar per sqm. discountcomposite. Unfortunately I am unable to get in touch with them by phone or email.

[apex1]

.
I guess that the kevlar will do nothing until the carbon is already broken. Right?


Cannot reply to your last question, I have no experience with both. But the assumption above is wrong, sorry. All the matrix, means every member of the matrix, has to carry the given load, simultaneously and transfer the load to the core and opposite matrix.
So, your Kevlar layer does´nt enjoy a boat trip, til the neighbour failed.;)

Regards
Richard

[sigurd]

Don't understand what you mean?
Transferring pressure from a sharp object directly into the core will ofcourse happen, but... I think what happens is that the fibers' tensile stiffness and strength is responsible for spreading the point load to a larger piece of core..?
If I used rubber instead of carbon, the rubber would be just pushed straight through the core without puncture. So with this assumption I conclude that "stretchy" kevlar will not delay the puncturing of the carbon, but it will delay the puncturing of the core.
Spectra on the other hand is almost as stiff as carbon so when the carbon is almost rupturing, the spectra is also almost rupturing, so both are protecting each other. make sense?

[apex1]

Don't understand what you mean?
Transferring pressure from a sharp object directly into the core will ofcourse happen, but... I think what happens is that the fibers' tensile stiffness and strength is responsible for spreading the point load to a larger piece of core..?
If I used rubber instead of carbon, the rubber would be just pushed straight through the core without puncture. So with this assumption I conclude that "stretchy" kevlar will not delay the puncturing of the carbon, but it will delay the puncturing of the core.
Spectra on the other hand is almost as stiff as carbon so when the carbon is almost rupturing, the spectra is also almost rupturing, so both are protecting each other. make sense?

Yes, if you like to describe it so.
What usually is´nt understood, is the fact, that you have no Kevlar or carbon, glass or whatsoever. You have a completely new material. The matrix, does neither behave like carbon nor like kevlar, it´s a complex mix of addition and subtraction of the different materials characteristics.
Naturally if you shoot at it (as an example of puncture), the outer carbon layer gets destroyed before the inner kevlar bears a load. If you now substitute the (softer) Kevlar with the stiffer (I dont know) Spectra, I would guess you pay for bacon and get belly. Now you have two materials in the matrix that are not as puncture resistant as the former combination, your matrix will fail sooner, not later! Although it was´nt wrong that both materials still are protecting each other, that was better achieved by the K/C combi.

I hope I could express that clear enough?

Regards
Richard

[Landlubber]

Basically what Apex is trying to say is that the sum of the two products is not equal to the sum of the individual products added together.

They form an entirely new substrate, the characteristics may not necessarily represent the addition of the individuals characteristics.

[sigurd]

Thanks for the effort, both, but I don't understand.

[Landlubber]

OK, I will try to do a better job.

If material "a" has certain charasteristics on its own, and material "b" has certain characteristics, on its own, then the combination of materials "a" and "b", need not necessarily be the same as the total of "a" and "b" individually, sometimes the characteristics are greatly improved above the sum of the individual parts.

[Landlubber]

Take for instance, a composite lamination of 300gsm CSM and 25mmfoam.

The two layers of 300, individually, are not very stiff (as an example).

The 25mm of foam is not very stiff either, but laminate one layer on each side of the foam, and the total stiffness is greater than the total stiffness of the sum of the individual parts.

[apex1]

Basically what Apex is trying to say is that the sum of the two products is not equal to the sum of the individual products added together.
Right, thank you
They form an entirely new substrate, the characteristics may not necessarily represent the addition of the individuals characteristics.
may not necessarily
No, they never do !
To try again, sigurd wrote: So with this assumption I conclude that "stretchy" kevlar will not delay the puncturing of the carbon, but it will delay the puncturing of the core
That exactly is wrong! You look at two materials, you do´nt have two! In your matrix the carbon fibre will hand over a lot of load to the kevlar fibre wich now acts as a bumper, spring, or so, giving the carbon fiber attributes she originally does´nt have! To a certain point! (very dilettantic, but I cannot express it better in english)
You look at say a Steel and a Alu plate connected. If you could amalgamate them, adding some copper and lead, you came out with a totally different material having nothing in common with the former.
Was that better?
Regards
Richard

[sigurd]

I think I get your point.
But, I wish I knew more about *how* the materials interact? If I knew, maybe I could deduce which combination would be preferrable? It seems like apex1 thinks carbon/kevlar is better, but I still find it a bit hard to conclude.

[apex1]

I think I get your point.
But, I wish I knew more about *how* the materials interact? If I knew, maybe I could deduce which combination would be preferrable? It seems like apex1 thinks carbon/kevlar is better, but I still find it a bit hard to conclude.

Yes, you´re right. Unfortunately my ability is´nt sufficient to calculate a matrix, I otherwise would have done already, to assist you, and to back my statements with some figures.

Regards
Richard

[sigurd]

Here is one drop test. (http://books.google.com/books?id=7oWlk5fI1A4C&pg=PA76&lpg=PA76&dq=spectra+laminate+epoxy&source=web&ots=otLT6Q8tMZ&sig=VgkKdz9LgR92jvD55EMs65dN_Mw&hl=en&ei=WzScScDwI8-g-gbesfXhBA&sa=X&oi=book_result&resnum=4&ct=result#PPA76,M1) I'm not sure how much real world impacts with a core relate to this.
edit: don't you think it's curious that the kev hybrid fails before the glass hybrid?

[sigurd]

Here (http://www.djaerotech.com/dj_askjd/dj_questions/fuse.html) is a chart for materials properties by themselves.

[apex1]

Here is one drop test. (http://books.google.com/books?id=7oWlk5fI1A4C&pg=PA76&lpg=PA76&dq=spectra+laminate+epoxy&source=web&ots=otLT6Q8tMZ&sig=VgkKdz9LgR92jvD55EMs65dN_Mw&hl=en&ei=WzScScDwI8-g-gbesfXhBA&sa=X&oi=book_result&resnum=4&ct=result#PPA76,M1) I'm not sure how much real world impacts relate to this.
edit: don't you think it's curious that the kev hybrid fails before the glass hybrid?

Interesting. The test setup looks pretty loopy, tipically "scientific" madness. Different impact velocity, not related to specimen thickness (wich is different for what reason?), or another obvious value ? Imho the footnote says manipulated, nothing else. Maybe I´m just too stupid to understand?
Worthless results.

[sigurd]

I'm not clear whether the impact velocity listed is the one where they considered the sample broken?

[sigurd]

Another UHMWPE application. (http://www.witchcraft.nu/techinfoseries.php)

[apex1]

I'm not clear whether the impact velocity listed is the one where they considered the sample broken?

Think so, but I´m not shure either. And why the hell different thickness, why "normalized" data? The specific energy to peak force could provide a good database, but "normalized" ? It is so easy (if you are not a scientist, teacher or lawyer), same size of samples, gives different velocity at impact before it brakes, proper result we could work with. nada...
very interesting data (and very clear) for the surfboard test.

Regards
Richard

[apex1]

Another UHMWPE application. (http://www.witchcraft.nu/techinfoseries.php)

Sigurd, if you understand some German, here is a download of the "LamiCens" Prog. Excel based and easy to understand. You can calculate every sort of fiber resin mix to very exact values! Must register and you have immediate access to the DL. Btw. their onlineshop (also in English) is really one of the best for the industry.

http://www.r-g.de/laminatberechnung_registrierung.html
and this is a REAL test:
http://download.r-g.de/rg_dokumentation_whz.pdf
unfortunately (for you) in German only, and no spectra.

hope I could help a bit.

Regards
Richard

[dccd]

The drive to use composites has always been to reduce weight in structures. That is probably why the testing is of different thicknesses, the samples are all of a common weight (see specific gravity). The example given of monolithic materials is less typical than the use of interwoven polymers (see image). Carbon has always been champion of stiffness, Kevlar and now Spectra better in tension. The science of the interaction among the fibers is probably less understood. However, think on the scale of the fabric where none of the threads are straight, they are like sine waves. if the yield (beginning to stretch) of carbon is less than its hybrid neighbor spectra, the carbon straightens out more. The Kevlar can yield and then add its better tension strength to the matrix. Hope that helps.

[sigurd]

Apex1, I'll check them out. don't understand german unfortunately.
Edit: I'm unable to shift from sheet1 to the other sheets in the spreadsheet..?

dccd, I don't see the correlation between specific gravity and the sample thickness in the "google book" test. I couldn't find the reference for how they made the samples.
The weave thing you explained sounds reasonable.
I don't know if the stuff witchcraft use is a dyneema/carbon mix or separate fabrics. For me it would be carbon uni (or rather tows) under spectra, if i can get it, I suspect these people only want to sell a 100yd roll and I only need 30yd. It is 4.1oz plain weave, 60" wide and 15.50 (us or canadian, not sure) per l.yd. if anybody is interested in chipping in.
I assume none of you read the "witchcraft" description of kevlar/carbon fabric, since it is on the "customs" technical page.

Carbon-Kevlar is fairly stiff and pressure resistent due to the carbon so a lighter inner build up of materials can be used. Pure carbon would be too stiff and uncomfortable for waveboards and pure kevlar too flexible. The Kevlar helps to reduce damage on impacts. On overloads the 50% carbon, because it is much stiffer than the 50% Kevlar, will take on most of the forces and can break easier as there is only 50%. Therefore this material is more suitable for sailors with a “controlled” sailing style.

I had never heard about "h-glass" - it is also described.

H-glass is a new patented microscopically hollow glass fibre. It is 40% lighter and 32% more pressure resistent (against creasing, usually the reason for board breakage) than traditional e-glass. H-glass based composites also serve as a very efficient shock absorber. A very good alternative for Dyneema, especially for spots without rocks.

I am assuming creasing is similar to buckling?

[apex1]

Apex1, I'll check them out. don't understand german unfortunately.
Edit: I'm unable to shift from sheet1 to the other sheets in the spreadsheet..?
You have to check the box in the middle, to agree with terms of use, then click the right box saying "Weiter". You could design and calculate a laminate then. Could.... if you understand German. Unfortunately, as i noticed, the guys "optimized" the program to work with their Products only!!!

I had never heard about "h-glass" - it is also described.

You´ll find H-Glass on the R&G website / onlineshop ! change language to English!

And YES creasing is buckling.
Some results of a sample laminate. Attached

Regards
Richard

[hardshell]

The third ingredient that needs to be considered here is the binder. Vinyl, poly, or epoxy resin will all add slightly different characteristics to your composite. Think of baking -- you mix a few ingredients together and they taste like the mixture that they are. Add a binder and some heat and you can get cake, cookies, or bread with only slight variables in ingredients.

[apex1]

The third ingredient that needs to be considered here is the binder. Vinyl, poly, or epoxy resin will all add slightly different characteristics to your composite. Think of baking -- you mix a few ingredients together and they taste like the mixture that they are. Add a binder and some heat and you can get cake, cookies, or bread with only slight variables in ingredients.

Ähhh..sorry hardshell, did you read this thread?...........:rolleyes:
But thank you anyway.

Regard
Richard

[sigurd]

You have to check the box in the middle, to agree with terms of use, then click the right box saying "Weiter". You could design and calculate a laminate then. Could.... if you understand German. Unfortunately, as i noticed, the guys "optimized" the program to work with their Products only!!!

Doesn't work, maybe because I use OpenOffice. Oh well.

Apex1, you make it so I have to go back and reread all your posts... often adding a little bit of help and info afterwards... :)

[apex1]

Doesn't work, maybe because I use OpenOffice. Oh well.
Well...
Apex1, you make it so I have to go back and reread all your posts... often adding a little bit of help and info afterwards... :)

Sorry, I have a very poor Internet connection here in Turkey, uploads can take as much as 30 minutes for 100kb, (Europe?!). So I post the reply and edit immediately to make the upload in the background. I know edited post can be annoying, sorry.

Regards
Richard

[sigurd]

No, not annoying

[sigurd]

What I wonder also is whether spectra/dyneema and also aramids have to be coated or treated to bind with epoxy. advancedcompositetraders is the correct link for the spectra I mentioned. They said it is compatible with epoxy.

[apex1]

What I wonder also is whether spectra/dyneema and also aramids have to be coated or treated to bind with epoxy. advancedcompositetraders is the correct link for the spectra I mentioned. They said it is compatible with epoxy.

Yes it is compatible, a test is shown on R&G website, but it is said also, that it is very difficult to cut and almost impossible to sand! The fibers and tissues that I found have no coating.

http://www.dsm.com/en_US/html/hpf/products.htm

http://www.swiss-composite.ch/pdf/t-dyneema.pdf

Regards
Richard

[sigurd]

So, I have compared the data we have collected so far about the fiber properties. Not much to go after, might as well throw a dice for column and one for row.
Are they talking about UTS (stress to failure) and tensile modulus of elasticity everybody?
Surprising that carbon has lower yield strength by an order of magnitude than S-glass.

[apex1]

So, I have compared the data we have collected so far about the fiber properties. Not much to go after, might as well throw a dice for column and one for row.
Are they talking about UTS (stress to failure) and tensile modulus of elasticity everybody?
Surprising that carbon has lower yield strength by an order of magnitude than S-glass.

Nice collection.Save money, you can throw the same dice for both decisions!!!
UTS, ultimate tensile stress, is stress to failure yes. Whereas modulus of elasticity, is the E- modul. The ability to carry loads of bending and compression.
PS what was it, you´re going to build?
Attachment: this laminate maybe what you want:
you know, there are coming 1 or two more, FINISHED!
Regards
Richard

[sigurd]

uh, think it was a boat...
looks like a nice program..
wonder why you put the carbon on the outside.. would it not be more vulnerable than glass?
biaxial 0' is the same as +-45' fiber direction right?

[apex1]

uh, think it was a boat... 1.
looks like a nice program.. 2.
wonder why you put the carbon on the outside.. would it not be more vulnerable than glass? 3.
biaxial 0' is the same as +-45' fiber direction right? 4.


Hello Sigurd,

1. no, really? And which sort of?:p
2. Yes it is
3. I see the laminate as a sandwich (just this example), so, hardest layer outside. And it made the most homogen layup. See graph above.
4. No, +- 45° is Bidiagonal. I used 0° Unidir. There are either +45°, or -45° Unidir., or Bidiagonal. available too. Example:

UNIDIREKTIONAL - GELEGE 0°
Unidirektional E-Glas Gelege 0°
BIDIREKTIONAL - GELEGE 0°90°
BIDIAGONAL - GELEGE ±45°
BIDIAGONAL - KOMPLEX - GELEGE ±45° + CSM
TRIAXIAL - GELEGE 0°±45°
QUADRAXIAL - GELEGE 0°±45°90°

If you would tell me wich sort of layup you are thinking of, I could run the calc. for you. To make it a reliable calculation, choose the material from R&G please, the program does not work with other products.

Regards
Richard

[sigurd]

I used 0° Unidir.
The pdf you sent says 90' bidirectional 310gsm glass. I figured it was +-45' because the graphs shows the best shear modulus in those directions?
It would also be more intuitive to me to put the glass in the same way as the sprectra, not the carbon, because of the compression strength.

I am going for a corecell laminate, at least for the most part.
I had figured that moduli and strength in tension and compression would be the limiting characteristics.
Looking at wikipedia, elastic modulus can be one of several moduli. I assume the one in the graphs, and the several tables above, are young's modulus: describing tensile elasticity. But you say it is for bending and compression.
The problem with R&G is they don't have wood veneer.
One could substitute corecell with their airex.
I think this should be a good place to start: The degrees signify fiber orientation. Outside first:
0' 600gsm wood
+-45' 150gsm dyneema plain weave (I haven't seen any dyneema in their webshop but you obviously have it in the program)
90' 100gsm carbon uni
4mm A600
45' 75gsm carbon uni
-45' 75gsm carbon uni
0',90' 150 gsm dyneema plain weave

A kiteboat. 6m long.

[apex1]

The pdf you sent says 90' bidirectional 310gsm glass.

A kiteboat. 6m long.

Hello Sigurd I´ll check that and try to calculate the layup, but have no data about the veneer at hand, can you provide some?

Regards
Richard

[sigurd]

Look at the last line in the table. It is snipped from http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf
Thickness is 0.6mm.
I made the program work in excel.
A windsurf board with 0.6mm pine surface: http://www.star-board.com/viewpage.php?page_id=16

[apex1]

Look at the last line in the table. It is snipped from http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf
Thickness is 0.6mm.
I made the program work in excel. Nice !
A windsurf board with 0.6mm pine surface: http://www.star-board.com/viewpage.php?page_id=16

Thanks, I have former source (the mech. properties of wood) on my Laptop, but had forgotten.
I wait in suspense what sort of layup you are going to design. Let me know here.

Regards
Richard

[sigurd]

I have come upon a great information well: http://www.sailboat-technology.com/links/online_articles.php
Currently reading the one about impact strength.
I think their conclusion about carbon being best in impact is rather surprising, although I am not well schooled on the subject. Later in the paper they seem to come to a different conclusion. I guess it depends on what is the first thing to fail, core or fiber. I bet with the harder cores like balsa, carbon will do relatively better on impact whereas the tougher fibers like S-glass may do better with corecell or airex?
I had wondered about replacing the 90' carbon with a somewhat heavier S-glass (or maybe h-glass), to match the elongation of the +-45' spectra and thus get a higher yield strength, and possibly better impact strength, but it supposedly fatigues more than carbon - has to be kept below 20% of yield vs carbon 60%. More on that in the link.
Just made some test strips with a yellow foam I have, not sure what it is, seems brittle.
May be ready for destruction tomorrow.
This here is 0' ipe, 90' 100gsm carbon, other side 0' 100gsm carbon and 90' makore.

[apex1]

Just made some test strips with a yellow foam I have, not sure what it is, seems brittle.
May be ready for destruction tomorrow.
This here is 0' ipe, 90' 100gsm carbon, other side 0' 100gsm carbon and 90' makore.

Let´s see what happens.
Why did you choose to lay the wood at 90° ?

[sigurd]

The first testing will be 3 point bending, a little, then turn sample, bend again, repeat until one of the sides fail. The 90' wood is because I did not want to help the 0' carbon on that side, to be more fair to the 0' ipe.
Outside of the impact testing it will have no effect I think.
I am pretty sure the ipe will fail in buckling before anything else - the 90' carbon under it is quite uneven.

I also made one with only 0' ipe and 0' makore on the other side.
And one with 0' 100gsm carbon one side and 0'/90' 4x100gsm plain weave glass on the other - 90' makore on both outsides.

edited glass weight.

[apex1]

understood.........
Regards
Richard

[sigurd]

I am sitting here destroying some pieces of laminate. Edit: now they are all trashed.

It is hand layed up epoxy and cured over night over an oven. The shopping bag stuck to the surfaces so is not a release film.
The test apparatus is a fine calibrated human made by Mom and Dad.
I can hear the core getting torn or its microbubbles collapsing with only a small deflection. Hope the corecell is a lot better. If anybody has any idea what this yellow foam could be please tell.

The glass is ridicolously soft even at 400gsm. Comparable to 230 gsm makore on denting resistance (protecting the core). I can press the laminate into the core with the thumb. The ipe can also be depressed but it is more difficult. The makore I can break by pushing it into the core but not the other two.

The wood/carbon samples can easily be pierced with a flathead screwdriver. It is "almost" not possible with the glass/wood and I can not do it with the plasma/wood except by aligning the driver so it slides between the uni fibers.

sample)

1) 0' 430gsm ipe, core, 0' 230gsm makore
seemed equally stiff either way.
makore buckled into the core.
tried to break it the other way afterwards, just got delam on the makore (tension) side. the samples are very short, and using only half the length of it (it was broken remember) would make this failure mode more likely.
thin layer of core left on the makore.

2) 90' 230gsm makore, 0' 100gsm carbon, core, 90' 100gsm carbon, 0' 430gsm ipe
seemed equally stiff either way. seemed to start buckling like 3) on both sides but I moved my thumbs apart to not excacerbate the buckling. ipe broke then in tension. Likely tensile properties of veneer is hugely affected by grain runout and other stuff. Afterwards, tried to break it the other way but got delam just like on 3)

3) 90' 230gsm makore, 0' 100gsm carbon, core, 0'/90' 4x100gsm glass plain weave, 90' 230gsm makore
seemed equally stiff each direction. Tried to avoid buckling by applying soft pressure over wide area with thumbs. Core sheared (?) and delaminated, not sure which came first.it just cracked, skins intact, the crack is in the middle between the thumbs and the fingers on the upper side of the sample. The delam is on the tension side.

4) 0' 230gsm makore, 0' 200gsm carbon, core, 0' 200gsm carbon, 0' 230gsm makore
delam/core shear

5) 0' 230gsm makore, 0' 200gsm carbon, core, 0' 200gsm plasma (enhanced spectra from puget sound rope), 0' 230gsm makore
delam/core shear

[apex1]

The test apparatus is a fine calibrated human made by Mom and Dad.
I doubt that! especially the ..fine...
I can hear the core getting torn or its microbubbles collapsing with only a small deflection. Hope the corecell is a lot better. If anybody has any idea what this yellow foam could be please tell.

most PU foam used in the construction industry is yellow with a brownish touch. Just rubbish.


If it´s simple assembly foam you used, you can assume to get much better results with corecell.
I wait until the test results are final.
R.
R.

[sigurd]

I'm pretty much done with them, there are only shrapnel left.
Both the ipe and the spectra results are encouraging except for the ipe tensile strength. I wanted to be able to relate it to carbon for strength in compression and tension (assumed I would need about 5-10 times heavier wood than carbon) as they should have a similar strain to failure (at least some species).
Now, the ipe will mostly be loaded on compression, being on the outside.
For the more global longitudal tensile loads, it is not so important whether the strength is on the inside or outside of the core, so the inner 0'/90' spectra will help (again, if I can get it). Also the bilge will get some more stuff on the outside of the core which can be longitudal.

Since I mostly got core failure the experiment was not hugely successful but it helped build a little bit of intuition regarding the materials.

[sigurd]

I have a question.
Consider a cored slender hull. You have one layer fabric each side. Obviously one of them should be 0'/90'. Does it make sense to skew the other to +-45' or is it better to keep the two layers in the same direction?

[apex1]

Does it make sense to skew the other to +-45' or is it better to keep the two layers in the same direction?

The answer is yes...............
I used Glassmat for core simulation, but the result is the same with foam core (not the figures naturally).

[sigurd]

Thanks, good idea. Doesn't seem unlikely to me. But i haven't seen any examples of laminates using different bias each side of the core. Have you?

[apex1]

No, Sigurd.
But that does not mean that much, you know I´m building in wood / EP only. So, what have I seen?

[sigurd]

Coal soot? Rot? :) I asked because I am getting a 180gsm 2/2 twill with 50/50 carbon/dyneema, which will likely be enough each side of the corecell (which is on its way!) for structure. If I only could remember what it was that I was going to build... Must have been something highly fashionable.

[apex1]

Coal soot? Rot? :) I asked because I am getting a 180gsm 2/2 twill with 50/50 carbon/dyneema, which will likely be enough each side of the corecell (which is on its way!) for structure. If I only could remember what it was that I was going to build... Must have been something highly fashionable.

You should read: HOW MUCH ABOUT THIS SUBJECT HAVE I SEEN!!! NOT TOO MUCH, AT LEAST NOT ENOUGH THAT IT WOULD COUNT!!!
was that clear?
Coal, soot, and rot, yes on my steamers I had enough of all.
On my production boats rot is no issue, we saturate the veneer almost completely. Coal and soot yes, fumes too, sometimes customers emit such stuff if we present the bill.
180gsm 2/2 Twill??? what means 2/2 in this case?
Cannot comment your last sentence, I still do not know what you are going to build!!!???

Regards
Richard

[sigurd]

I understand. 2/2 twill means 2 over, one under, 2 over, etc in the weave - in both directions.. 0' and 90'.
From what I read, such weave is looser, but more easily conformed to curves, than plain weave (over, under, over...) The fibers also gets less kinks than PW - making it more fatigue resistant and giving it more compression strength.
http://www.sollercomposites.com/fabricchoice.html

[apex1]

I understand. 2/2 twill means 2 over, one under, 2 over, etc in the weave - in both directions.. 0' and 90'.
From what I read, such weave is looser, but more easily conformed to curves, than plain weave (over, under, over...) The fibers also gets less kinks than PW - making it more fatigue resistant and giving it more compression strength.
http://www.sollercomposites.com/fabricchoice.html

Thanks I got it, come back to subject later at night.
Regards
Richard

[sigurd]

If you are interested in further opinions on the subject of asymmetric laminates, see this SA thread. (http://forums.sailinganarchy.com/index.php?showtopic=87119&st=0&gopid=2178697&#entry2178697)

[lymanwhite]

Interesting information. We used kevlar as an abraison layer just inboard from the outer skin, on the main hull of a carbon over end grain balsa tri.