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Cuben Fiber Meet My Tensometer!
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Chris Lucas
(ChemE) - F

Locale: SC
Cuben Fiber Meet My Tensometer! on 07/14/2010 20:11:43 MDT Print View

And so it begins...
Testing Cuben Fiber

Chris Lucas
(ChemE) - F

Locale: SC
The Details on 07/14/2010 20:16:18 MDT Print View

It is still very early days but for anyone interested in the details, this is 0.33 oz/yd² Cuben fiber from Quest Outfitters. The strip you see in the tensometer jaws is precisely 1 inch wide and the whiter area in the center is a 1 inch by 1 inch overlap bonded with 45 milligrams (yes 0.045 grams) of our solvented moisture-cured polyurethane. The strip broke at 17 pounds force and the bond was totally unaffected. I'll experiment over the weekend with progressively smaller bond areas until the bond becomes the failure point. I'll also do peel adhesion tests, this is tensile shear adhesion.

Edited by ChemE on 07/18/2010 07:45:02 MDT.

Christopher Holly
(climber72) - F

Locale: At my desk
nice... on 07/14/2010 20:56:48 MDT Print View

The geek in me just giggled! Very cool idea, can't wait to see the data!

Steven Evans
(Steve_Evans) - MLife

Locale: Canada
Re: Cuben Fiber Meet My Tensometer! on 07/14/2010 21:08:19 MDT Print View

This is absolutely amazing. I can't wait to see all the results!

If I read the cuben fiber spec sheet properly, a 1" strip of the 0.33 cuben should break at 35 lbs. Correct? So with the overlap bond, it is currently breaking at about 50% of the spec. Any chance you can test a piece without a bonded area just to see what it will break at?

I (and probably many others) will be following this thread closely. A big thanks in advance for posting this type of info for the community to learn from.

Chris Lucas
(ChemE) - F

Locale: SC
I did already on 07/14/2010 21:12:08 MDT Print View

Hey Steve, I was hoping you would join in on this thread, glad to see you here already. I tested 5 strips without a bond and all broke at 15-18 pounds force. The alignment in the tensometer jaws was perfect and the failure mode was a sudden catastrophic failure rather than a progressive tear which would indicate poor alignment. A representative picture of the failure mode is below.

Close Up of Failure
Cuben Failure

Besides, any strip which fails at a spot other than the bond might as well be non-bonded for purposes of characterizing the Cuben fiber itself right?

Edited by ChemE on 07/14/2010 21:22:25 MDT.

Sam Farrington
(scfhome) - M

Locale: Chocorua NH, USA
tensometer on 07/14/2010 22:08:25 MDT Print View

Could you try some strips of other fly fabrics, like TH silnylon and spintex, for purposes of comparison?

/A .
(biointegra) - MLife

Locale: Puget Sound
Re: Cuben Fiber Meet My Tensometer! on 07/14/2010 22:19:59 MDT Print View


This is fantastic. Thanks for sharing with the community. I am looking forward to seeing the data and would be happy to send you some test swaths of varying weights of cuben scraps and would encourage anyone else to do the same in order to get a more accurate scope of figures from multiple random batches. Depending on the size required, I may have some well used material to supply for comparison, if it would be of any interest to you. Judging by the photograph, the 1" strip looks to be approximately 12" in length, including what is presumably well in the clamp. Am I close?

Did you perchance weigh the fabric samples in order to see if they were true to spec?

Thanks for posting photos as well!

Scott Van Doeselaar
(vandoe) - MLife

Locale: Southern CA
Re: Cuben Fiber Meet My Tensometer! on 07/14/2010 23:33:57 MDT Print View

Very nice. It is great to see quantifiable results.

You mentioned "our" polyurethane. Can you shed any more light on this bond material and its characteristics?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Cuben Fiber Meet My Tensometer! on 07/15/2010 02:03:45 MDT Print View

Hi Chris

Tinius Olsen?

Interesting (or curious) that the specimens did not fail at the edge of the clamp.


Chris Lucas
(ChemE) - F

Locale: SC
Happy To Test Other Materials on 07/15/2010 02:04:27 MDT Print View

Sam and Aaron: If anyone would like me to get the true mass and tensile strength of other fabrics, I'm perfectly willing to do so.

Aaron: You are incredibly close, the samples I was cutting were 12.5"x1" by in truth I'll probably switch to 6" long samples since this is still plenty long. And yes, the fabric was first weighed to the nearest milligram to establish its true weight.

Scott: I'm not quite ready to disclose which adhesives I'm using but suffice it to say that Loctite is one of our low-cost (and extremely low performance) competitors. Our materials are more expensive but typically much higher performance as compared to Hysol and other commodity epoxies.

Roger: Japenese indeed, it is a Shimadzu 10,000N rig. The jaws are 100% American designed and fabricated though.

Edited by ChemE on 07/15/2010 02:06:33 MDT.

Derek Goffin

Locale: North of England
Cuben Fiber Meet My Tensometer on 07/15/2010 02:59:02 MDT Print View

this is a high tech and hopefully more accurate trial of cuben than my basic attempt with rope, cramps and a bucket of sand attempting to do the same thing. My results are not too far out of line with yours. However all of my failures were at the edge of the clamped area, the edge of the glued area, or failure of the glue bond itself. Were your failures elswhere?
Your results are not anywhere near the cubic tech figures. I Wonder how they get such high results? Maybe the forces in my setup were more in line than I thought.

Chris Lucas
(ChemE) - F

Locale: SC
Failure Locations on 07/15/2010 04:45:15 MDT Print View


So far all failures have been in the middle of the fabric itself perhaps an inch below the bottom of the top jaw. To me this means that was the weakest line in the strip of fabric under test and the tensometer jaws are not stressing the fabric. Keep in mind that these machines are quite expensive and for precisely this purpose so this result doesn't surprise me at all. Why would the fabric fail at the edge of the jaw/clamp unless that area of the test setup is concentrating force? Sure once or twice that might honestly be the weakest spot of the fabric but surely not every time.

The two epoxies that I wanted to try have been curing for 24 hours so they'll get tested today too when I get in to work. I expect that each of them will add more weight than did the MCU and I would be shocked if either failed in the bonded area. We'll know soon enough.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
nice work... on 07/15/2010 06:11:25 MDT Print View

> Interesting (or curious) that the specimens did not fail at the edge of the clamp.

Most tensile test specimens have widened ends and taper down to the actual test area, so I was expecting a doubled-thickness or something at the jaws. But if the samples aren't failing at the jaws, then it sounds like the methodology is fine, and the jaws aren't having any effect.

I'd guess that the failure is due to microtears in the fabric along the edge, as a consequence of the strip cutting process. One might expect this to cause a propagating failure, but it may be that the rip occurs so suddenly that the propagation isn't visible to the naked eye.

Good to hear that the bonds hold up well. I guess a peel test is next...?

Marco A. Sánchez
(marcoasn) - M

Locale: The fabulous Pyrenees
Re: Cuben Fiber Meet My Tensometer! on 07/15/2010 06:44:56 MDT Print View

Very interesting, but…

“I'm not quite ready to disclose which adhesives I'm using…”

If you don't tell us what adhesive you used or it isn't available to us (MYOGers), then what’s the point of the experiment?


Steven Evans
(Steve_Evans) - MLife

Locale: Canada
Re: Re: Cuben Fiber Meet My Tensometer! on 07/15/2010 11:15:28 MDT Print View


Edited by Steve_Evans on 07/20/2010 10:15:02 MDT.

Dan Durston
(dandydan) - F

Adhesive on 07/15/2010 11:44:13 MDT Print View

What would make one adhesive better than another, if both are strong enough that failure doesn't occur at the bond? I don't understand the criteria for what makes a high vs. low performance adhesive.

Edited by dandydan on 07/15/2010 11:44:47 MDT.

Steven Evans
(Steve_Evans) - MLife

Locale: Canada
Re: Adhesive on 07/15/2010 12:09:47 MDT Print View

Well said Dan.

I have no problem if Hysol is in fact low performing, I'd just like to see why/how it is. Maybe the peel testing will show a significant difference...just guessing.

Kevin Beeden
(captain_paranoia) - F

Locale: UK
re: the point? on 07/15/2010 12:33:22 MDT Print View

> If you don't tell us what adhesive you used or it isn't available to us (MYOGers), then what’s the point of the experiment?

To show progress in the development/testing of an adhesive suitable for Cuben? From Chris' comments about competitors, it's pretty clear he works in such a field.

Whilst I guess I'm used to manufacturers downplaying their competitor's products, I'd like to think that we can keep that sort of stuff out of a MYOG section, and echo Steve's comment that such adverse comments should be backed up with test results, or not made; after all, we don't generally care who we buy our materials from, just that they work.

Chris Lucas
(ChemE) - F

Locale: SC
Fear Not on 07/15/2010 12:34:41 MDT Print View

The adhesives that I'm using are available anywhere in the world though not through retail channels. Only from Distributors. The reason I've not posted information on the adhesives I'm using is because I'm not sure they're better for this task, I'm very sure they're more expensive, and I have only just started to characterize our products in this application. But for those who just can't wait, I've gotten the best results with Belzona 2911 (Elastomer QD Conditioner). Solvent appears to be an important component with cuben though. The non-solvented expoxies didn't perform nearly as well as did the solvented MCU (the 2911).

Steve, I wasn't bashing Loctite (or at least didn't mean to) only saying that I might be able to get more adhesion per weight.

Steven Evans
(Steve_Evans) - MLife

Locale: Canada
Re: Fear Not on 07/15/2010 15:59:24 MDT Print View

Aha! I knew it was Belzona. I did a little digging and your name popped up along with that company. :)

As for Hysol, as of right now AFAIK, there is not a better way for the MYOG'er to bond cuben fiber. My experience with it has been great. It's readily available, affordable, no bond failures, requires no training (ie. anyone can do it), needs only a brush...I could go on. One of the only downfalls to it is that it is a bit of a pain to apply it especially on the longer sections.

So, I just wanted to make sure that if we are going to categorize the Hysol as low performance, that we come up with something better and share it with the community.

By now most of you guys know I'm a full on nerd and love this type of stuff so I really appreciate the time you're putting in. I'm very interested in the project and this thread has the potential of containing great information for people to lean from.

I'm taking off for the weekend but I'll catch up with you guys when I get back. Good luck on the tests.

Edited by Steve_Evans on 07/15/2010 16:00:01 MDT.