Cuben Fiber Meet My Tensometer!

[Chris Lucas]

Hmm, good idea. We'll know in about 15 minutes.

I just ran 3 6"x1" samples cut 90 degrees to my initial population because I noticed that the spectra fibers appear to be more dense in one direction that the other. These samples averaged 28.7 lbf which is 82.1% of Cubic Tech's claim. I'll try folding the edges as well…

[Tim Marshall]

if the edges are folded then wont the force be on a double layer and not on the single layer? I am not technical like you guys so i could be way off, but it seems to me 2 layers is stronger than one so if we're trying to find the strength of 1 layer folding it to a double layer even on the sides will distort the results won't it? I am very open to being wrong, that is just what i am thinking.

-Tim

[Chris Lucas]

So folding the 1" samples in thirds made it WAY easier to load it in the jaws perfectly vertical and evenly tensioned. I just got a result of 36.8 pounds force which exceeds Cubic Tech's claim. Now to run three duplicates to confirm that this isn't a spurious result…

[Chris Lucas]

Tim,

I'm fairly certain that folding won't change anything. The amount of material available to support the load remains unchanged so each spectra fiber shares the load equally. What folding did just do was evenly tension the entire piece simultaneously. Without folding no matter how much I fiddled with the sample there was always one edge which became taught before the other. That or there would be ripples which tells me that things aren't being tensioned uniformly despite my efforts to the contrary.

[Chris Lucas]

"I am not technical like you guys so i could be way off"

You may not be technical but you make bad ass quilts!

[George Geist]

> So folding the 1" samples in thirds made it WAY easier to load it in the jaws perfectly vertical and evenly tensioned. I just got a result of 36.8 pounds force which exceeds Cubic Tech's claim.

Hi Chris,
Thanks for confirming my guess that Cubic Tech's strength results were without edge effects. Mylar is prone to catastrophic failure if a small (even micro) tear gets started. What is so great about your results is that it shows folks doing MYOG with Cuben how strength can be compromised without careful consideration of where tears can start.

[Chris Lucas]

So I tested a 6" peel adhesion sample this morning and the 2911 is very poor in peel adhesion. The maximum force I recorded was 1 pound force which to me is totally unacceptable.

Peel Adhesion Setup

It also appears that the solvent in the 2911 attacks the mylar film, the spectra fibers, or both. I noticed yesterday while fooling around with minimum bond overlap that the samples overwhelmingly tended to break on either side of the bond area. This was my first hint that the solvent was weakening the fabric. To confirm my suspicions I made a small population of controls and a small population that got a very thin coat of 2911. The 2911-exposed samples broke at 20 pounds force where the controls broke more in the 28-29 pound force range.

I've ordered some cuben tape from Quest Outfitters and I'll perform the same battery of tests with it. The only good things I can say about the 2911 are it has a nice long open working time (20 minutes or so), cures completely in 4 hours, has very respectable tensile shear adhesion, contributes virtually no weight (15 mg per inch @ 0.25" overlap). Down sides are a slight weakening of the fabric and miserable peel adhesion.

[Dan @ Durston Gear]

Great research. Interesting to see you've observed the adhesive weakening the material.

[Steven Evans]

….

[Kevin Beeden]

I agree that folding a sample is an acceptable method; provided you don't change the total cross-section area of the test piece, you still have the same stress on the material. Provided, of course, the folded test piece remains uniformly loaded across the entire folded width.

As Al says, the fact that your initial tests showed early failure gives users an idea of the limitations of practical production techniques, and may demonstrate how to overcome them; for instance, ensuring all edges are folded and bonded to ensure no micro-tears are exposed to propagate catastrophic larger tears.

Good stuff.

[Roger Caffin]

> ensuring all edges are folded and bonded to ensure no micro-tears are exposed

Very good point!
Very different from silnylon.

Cheers

[Lawson Kline]

Removed!

[Mark Fowler]

Thanks for the great information.

If I am reading you correctly what we have is a ranking of cuben seaming methods that can inform our design process.

The practical application of the results indicates that it is best to use a single piece of cuben rather than bond two pieces if possible. In second place is to use a Hysol bond with a strength loss of 45%. This is followed by well adhered taped seam with and without sewing and finally a purely sewn seam.

So the result is – use a Hysol glued seam but allow for the resultant loss of strength when specifying the fabric.

Subject to finding a better adhesive we have to live with these constraints.

[Marco A. Sánchez]

“what we have is a ranking of cuben seaming methods that can inform our design process”

Different materials, different solutions. I think we have much to learn about cuben.

Perhaps we should look more seriously how sailmakers work?

[David Olsen]

The glued bond sounds like it is not allowing transfer of
force equally along the bond in the direction of the force.
Similar consideration is needed in sewing fabric.

The direction of the seams, the length of stitch, the characteristics
of the thread, the number of rows of stitching, and the
stitch pattern, can also make a difference on seam strengths.

For example, using a stretchy thread could transfer more
force over a greater area, increasing seam strength.

Polyester thread has low stretch characteristics.

[Steven Evans]

….

[Steven Evans]

"Perhaps we should look more seriously how sailmakers work?"

I think the sail makers guys have their technique down pretty good, but from what I have seen on the net, they use expensive methods and tools. I think it was Chris or Roger who gave me the lead on the venture tape, mentioning that sailmakers use it quite a bit. I've been inpressed with it so far.

[Lawson Kline]

Hey Steve,

If you could also tell us how Ventura super seam stick performed in testing against Hysol and something like a 3M 9485PC.

In addition to that if you could also provide the forum with.

What weight cuben fiber did you use for testing?

What width tape did you use for testing?

What bonding techniques did you use?

What type of tests did you perform (i.e. lap sheer, 90 degree peel)?

How many tests did you perform?

What type of equipment did use for testing?

What % of the cuben specified load did the ventura taped seam fail at?

What % of the cuben specified load did the 3M 9485 PC taped seam fail at?

Did the carrier effect the ventura tapes performance?

Which tape is superior and why?

How do the tapes compare to Hysol?

I did my own testing so I would like to compare notes.

[Steven Evans]

…

[Lawson Kline]

Answers to my questions

>>>What weight cuben fiber did you use for testing? CT1K.08, CT2K.08, CT3.5K.18, CT5K.08, and CT5K.18… I tested CT2K.08 the most since it will be used in 90% of all my future products.

>>>What width tape did you use for testing? 1/2", 3/4" & 1"

>>>What bonding techniques did you use? Several… To achieve the best bond, make sure the surface is clean using either a heptane or isopropyl alcohol.. After bond has been completed heat the bond to 130 degrees while applying pressure will help to develop a much stronger bond.

What type of tests did you perform (i.e. lap sheer, 90 degree peel)? Both lap sheer, 90 degree peel and a 45 degree axial peel.

How many tests did you perform? Atleast 10 per material, adhesive type and bonding technique.

What type of equipment did use for testing? A homemade machine that uses wood clamps and water for weight. In order to load the test strips consistently I measure fill times to make sure the gravitational acceleration is all the same.

What % of the cuben specified load did the ventura taped seam fail at? 1" wide seam failed at 29% (30 lbs CT2K.08) without heat and 33% (35 lbs CT2K.08) with heat and pressure after 7 days.

What % of the cuben specified load did the 3M 9485 PC taped seam fail at? 1" wide seam failed at 35% (37 lbs without heat and close to 40% (41 lbs CT2K.08) with heat and pressure after 7 days.

Did the carrier effect the ventura tapes performance? YES… It has pros and cons. It helps for seam deflection but also makes the tape less conformable.

Which tape is superior and why? I personally believe the 3M 9485PC is the overall winner due the added strength and flexibility. Ventura Super Seam Stick is a great hi-tack tape and is cheaper. It will work better then the 3M 9485 PC in certain applications.

How do the tapes compare to Hysol? Hysol is strong but I am not a fan of it. It takes way too long to cure, its hard to use with curves and it creates a hard spot in the material. A Hysol seam fails around 50% (52 lbs CT2K.08), right next to the edge of the seam. I have never said not to use it but I have said it's not the best adhesive out there due to all its limiations. The common misconception is that a Hysol seam is stronger then the cuben fiber material itself which is not true at all. There is no way to create a seam that is stronger then the cuben fiber laminate because all tapes and adhesives bond to the Polyester film surface and not to the Dyneema fibers. A great alternative to Hysol is a good quality contact cement. Its much cheaper, stronger and alot more flexible. The bond will fail at close to 60% (62 lbs CT2K.08) BUT BE VERY CAREFUL USING THE STUFF. ONCE THE TWO PIECES TOUCH THEY CANNOT BE PULLED APART AND IF YOU TRY YOU WILL DELAMINATE THE CUBEN FIBER RUINING THE MATERIAL AND YOUR PROJECT. I STRONGLY CAUTION ONLY USING CONTACT CEMENT FOR SMALL THINGS LIKE CORNER TIE-OUTS.

The best bond I have been able to achieve will fail at around 77% (80lbs CT2K.08) and uses a combination of proprietary methods and materials that I will not currently disclose. I might sell the bonding system on my website at a later date but that will be determined down the road when I can judge if there is a demand for it.

[Roger Caffin]

Hi Lawson

You may have noticed my posting to Chris Lucas a little while back. I suggested to him that he might like to extend his tensile testing a bit and make an article for BPL out of it. Perhaps you could consider cooperating with Chris and combining the work the two of you have done in an article? I am sure all our MYOG fans would be fascinated and appreciative.

I can help with the writing editing etc IF needed.

cheers

[Steven Evans]

I realize now that you guys are doing the article that I guess I should hold off on questions and comments. My question was about heating the bond, but feel free to disregard. I was using an iron with the tape but never tried it on the hysol – wasn't sure if that's what you did.

And thanks for the info, I'm being serious, very interesting and much appreciated.

[Chris Lucas]

Ok, I've been super busy at work and totally beat when I get back to the hotel at night so I've held off commenting until tonight in hopes that this might go away…

@Roger: for sure I will write this up and extend the work into an article provided some fellow hobbyists can help me out by donating Cuben scraps, tapes, etc. I don't mind spending a little of my own money but would prefer to not spend a few hundred (easy to do at $30/throw for Cuben weights). It would already seem that there are plenty of inquisitive souls who are only too happy to help so no worries. I'll respond to your email with more details shortly.

@Steve: I respect your unwillingness to engage in a quarrel from another thread here, Kudos to you Sir.

@Lawson: It is clear to me that you have much to contribute to this very interesting subject and have already thought about a lot of the interesting questions which we all would like answered. It also seems like you might like to rib Steve if at all possible or at least some stuff comes across that way. I sure would like this thread to stay more or less on topic and be a technical discussion among peers (nerds, let's be clear). I'm not a mod so I can't enforce anything, just a request for professional courtesy. I would love to have all cottage gear manufacturers here and guide the research. I want your stuff to be even better so I have more reason to buy it.

If I came across in the above as less than eloquent or abrupt, please blame it on the two 9% abv beers I had at dinner rather than being a jerk. With that said, let's geek it up folks!

[Lawson Kline]

Hey Roger and Chris,

I wouldn't mind providing test strips if Chris is interested in doing the testing using his state of the art tester especially if it can accurately test peel. I could do the testing on my machine but it wouldn't be nearly as accurate or consistent as yours. I think to maximize testing, only one weight material should be tested. My vote is for CT2K.08 .75oz since it's the most commonly used material.

[Chris Lucas]

Lawson,

I agree that it appears to be the most common but I wonder if it is massive overkill for a great many projects. It seems to be that more wasteful but smarter cuts of 0.33 or 0.45 that stress the fabric on the warp or weft can work rather than chucking more weight at the problem. I probably haven't fried as many dollars worth of Cuben as you have so perhaps I'm just being naïve. Do we really need to use as much 0.78 as we do?

EDIT: changed "have" to "haven't"

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