Unidirectional Fiberglass

[Inquisitor]

Can anyone give information and/or advice on unidirectional fiberglass? I am new to working with cloth, fiberglass and room-temperature cure epoxies. I am most familiar/comfortable designing/building with prepregs in just about every other fiber. I want/need some better properties, but don’t need the performance step nor the cost of Carbon!

I have been scouring the Internet and have found very little information. So far I have found references to 7721 and 7715. I have a sample of the 7715. (picture attached, second layer is not uni) The fill fibers are still woven and I’d estimate about 20% of the “cloth”. I also have found a truer uni at http://www.aircraftspruce.com/catalog/cmpages/s2tape.php. It appears it uses some kind of non woven fiber bonded to keep the fiber relatively parallel. Comments regarding the following are desirable:

• Other brands/models of unidirectional fiberglass
• How easy to wet out compared to standard cloths
• How realistic it is to keep the fibers strait and parallel while squeegee-ing the hell out of it
• Vendors
• Relative percentages of uni versus fill fibers
• Properties
• Anything else, you might think desirable for designing/building with this material.

I know Properties are the hardest to find due to liability issues and/or cost/effort that someone had to go through to get them. I am willing to fill out non disclosure, wave liability or what other forms you might require to get them. I WILL be testing my chosen materials and getting my own properties… I would be willing share those properties back if prior arrangements are made.

Thanks for your help.

 

[Raggi_Thor]

You will find some information at Devold AMT,
http://www.amt.no/products.asp?page=1607&lang=2

I don't think they use S-glass though.

 

[nero]

Cofab?

This is where I bought several rolls of 10.oz uni and biaxel. It was the best price I could find. They drop shipped direct from the factory. Shipping was around $200 flat rate.

http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Knitted_Fabrics/knitted_fabrics.html

The factory is in South Carolina ... i think. The name on the rolls is Cofab ... if my memory serves me correctly.

It wets out easily with the thin and thick epoxy I use. The thick takes a bit of time to soak in so mostly, I use the thin epoxy to laminate with and the thick to fill in the voids. I have wetted out 2 layers of uni and 1 layer of biaxel over uncoated strip planking. Everything worked fine. Destruction tests have the delamination in the wood just below the resin line.

The yarns are not twisted and flat as the cloth comes off the roll. When it wets out the yarns seem to pucker up. Squeeging and pulling excess resin is straight forward ... no side to side or the fibers get curved. The stitching holds the yarns relative to each other so pulling back in the opposite direction gets everything straightened out again. The fabric will stretch in a sheer to conform to curves etc. Not terribly difficult to get it oriented the way you want using the dry method.

The rolls 50 inches wide. I work with up to 4 meter long lengths by myself.

If you can vaccume bag this or press it after you have worked in the resin the laminate will be thinner. On flat pannels, I use release film, scrap pannel pieces and a 10 inch cement block(s) to keep the seams flat. Works well.

 

[rxcomposite]

Inquisitor,
Be careful about using uni fibers because its strength is in one direction. If you are laying up several layer, lay uni in a +45, -45 degree angle or 0, 90 angle.Fibers dont have strength when it is pulled in a 90 degree direction of the fibers.

Unis are best used as reinforcing caps (one direction) on tophat stiffeners where the stress is either tensile or compression. The properties are further enhanced because at the top of the hat, it is farthest away from the neutral axis. Consider unis as special use fibers. Get the stiched variety.

Biax works well as the strength is in two direction. Remember to interspace biax with a thin layer of chopped strand mat to promote adhesion between layers and prevent voids.

If you can get biax with a thin layer of mat bonded in, much better. as it drape easy on flat surfaces. Loosely woven fabrics drape well on compound surfaces but you will have problem on flat surfaces as it tends to pucker up.

 

[spank]

You shouldn't need Chopped matt if you're using epoxy for the resin

 

[Doug Lord]

Carbon why not?

It seems to me that if you're going to use epoxy resin you'd be far better off using carbon uni and /or woven since the physical properties of the two together are probably a better match. S glass unitape is 2.10 per foot of 12" wide and carbon uni tape is 3.35 for the same thing in my catalog. It's definitely more expensive but is it really since you'll need less of it and you're already using epoxy?
Note that for glasing something like bulkheads to the sides/bottom you might want to use a 45° tape of either carbon or s- glass or a combination of the two.
From a cost standpoint you could probably achieve close to the same properties using s-glass and vinylester as you would with epoxy and s-glass or E glass...
---------------
Two books that might help are:
"The Elements of Boat Strength" by Dave Gerr and "Marine Composites" by Eric Greene and Associates

 

[Robjl]

Unidirectional

G'day Inquisitor,
You've probably seen the construction method for the unstayed mast for the proa at http://www.harryproa.com/building_hg/buildinghg_wk14.htm but if you haven't the construction method is well illustrated.
I thought it may help you get the unidirectional in your beams with limited mould necessary.
Regards.

 

[yokebutt]

If you are using a slow enough resin, then unidirectionals make a great "lowest common denominator", i.e. instead of getting things like biaxial tape for tabbing, you can achieve the same thing with unis.

Yoke.

 

[Inquisitor]

Saying no to carbon... so far!

I’m familiar (way too) with the negative aspects of unidirectional, however, it was definitely worth mentioning so that anyone who reads this thread might have those warnings. Thank-you. You are correct… I will only be using it in various beam-like structures. I will have adequate amounts of off axis plies required to keep the caps cohesive and webs strong enough for shear strength and local buckling.

As far as price…

So far, I have found this unidirectional 7721, 6oz/yd^2, 37” wide at $2/linear yard. It is E glass, however, the beams I am designing are stiffness critical, the added strength (and cost) of S glass are not necessary.

Although, I have not done an extensive search on carbon fiber pricing, a cursory glance shows that for unidirectional material of comparable width and thickness would be in the ballpark of $20 to $30/yard. I may be forced in this direction, but I will analyze it to death long before I open the wallet that much!

As far as epoxy versus vinyl ester, I am more familiar with epoxy (high temperature prepreg). I have not done any extensive comparison, however, the strength, impact strength, osmosis issues gave the nudge toward epoxy. Comparing prices at USComposites epoxy was at ~$37 per gallon. Vinyl ester at $36 was not enough lower to encourage me to pursue it further over my familiarity with epoxy.

 

[Doug Lord]

epoxy

IQ,I'd look carefully at the quality of any epoxy you get for those prices. Check out West System and Sp epoxies and I'm sure you'll find quite a difference(like twice) in the cost of a high quality epoxy vs a high quality vinyl ester.Also check out Aircraft Spruce for MGS resin. I'd rather work with epoxy myself but be careful: theres a lot of variance in quality and $30 a gal esp if that includes hardener just doesn't sound like something to use structurally in a boat....Also note that many boat companies use vinyl ester resin over gelcoat in a mold for the first one or two layers of glass followed by with regular isothalic polyester. The vinyl ester is an effective water barrier virtually eliminating osmosis.This is a cost effective solution but I would use epoxy on my boat. Just be sure to get good quality stuff.

 

[Inquisitor]

IQ,I'd look carefully at the quality of any epoxy you get for those prices...

You bring up a very important point! I did the price comparison to West System and System Three who were both within spitting distance of $100/gallon. I do wonder at why USComposites is so much lower. I searched the threads on this site and Learpilot has brought it up several times and no one has shot it down. A search on the Internet didn’t bring up any pros or cons. Surprisingly, I thought there were several negative comments about West.

Since my current project is only research, I think I am going to try it. I’ll be able to do most of the short-term (strength and stiffness) tests, but I’m am concerned about the long term issues. Noting in my other posts… differences of tens of percent, I won’t even bother... get the better. But factors of 3 or 10… I have to consider. For this project, I’ll go cheap and see where it leads. The next project (a 40’+ boat) with tons of epoxy… a factor of three will be more than noticeable! A WAG might be $20K versus $60K… in epoxy costs.

Could (possibly) bad epoxy be significantly worse than good vynel? I'm not qualified to comment. Maybe there is a polymer chemist on this forum that might could shine some light on the subject!

 

[nero]

The uscomposites epoxy is EPON resins and hardners. EPON has a websight with all the technical info needed. If you buy a 55 gallon drum prices fall to around US$ 22 per gallon of resin/hardner mixed. It may blush slightly. The medium hardner smells just like WS205.

The reason it is less expensive is EPON is the manufacture of it's resin. West Sytem and the other marketed brands are buying this resin from EPON and others big companies and mixing in other chemicals. Or they are simply having EPON mix it. The cost break comes into having less middleman and less marketing costs.

If you bought a railroad tanker full of this stuff I would cost less than Pepsi! smile

No, I don't get kick backs from uscomposits. There are other distributors for the EPON. They are listed on the EPON site.

 

[rxcomposite]

You shouldn't need Chopped matt if you're using epoxy for the resin

The epoxy resin or other type of resin has nothing to do with the biax. It is more on what you want to achive with laminate design.

Hexcel sells biax with a thin layer of mat. Others prefer woven fabrics but lay up a thin strip of mat on the edges to prevent the edges from curling up.

Mat can be a blessing as it built up bulk easily. In laminate design, bulk is sometimes needed to gain stiffness.

 

[rxcomposite]

The reason it is less expensive is EPON is the manufacture of it's resin.

I agree with EPON. It was introduced to us by Shell petrochemical company. It is cheap compared to other brand but the quality is good.

It is a base chemical that is used by the paint company selling epoxy paints.

The only thing you have to ask for correctly is the hardener. One type of hardener is toxic and is to be handled with care.

 

[Doug Lord]

Mat

Forget mat with epoxy; if it's not specially treated specifically for epoxy it won't wet out.