spectra vs kevlar?

Originally Posted by sigurd

Here is one drop test. 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.

Originally Posted by sigurd

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

Originally Posted by sigurd

Another UHMWPE application.

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?

Originally Posted by 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..?
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.

Originally Posted by 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.

Ähhh..sorry hardshell, did you read this thread?...........
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...

Originally Posted by sigurd

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.

Originally Posted by 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.

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