I know that cottage manufacturers and experienced posters to this forum seem to favor the heavier styles of cuben (CT2K.08, for example) for large tarps for the sake of durability, but I can’t help but wonder if lighter styles might be serviceable. So, I thought I would see if I could come up with a tarp that uses a light cuben but has robust enough seams, edges, and tie-outs to be durable.

I purchased 9m of the 0.48oz CT0.6K.08 material in “black” from cubic tech, and I decided on a 9’ x 9’ design. One of the things I plan to try is a sandwich-style seam along the ridgeline.



Also, it seems to me that some of the tensile forces on the material in a square tarp, due to the positions of the tie-outs, are on the diagonal (not aligned with the fibers). If the material were to actually burst under load, it is more likely to happen when the load is borne mostly by the film (when the forces are not aligned with the fibers). In a sail, the cuben would be cut into a series of panels and oriented so the fibers are better aligned with the tensile forces. I guess we don’t do that with tarps because we have an interest in minimizing the number of seams (also we don’t need a curvacious 3D shape). However, back when Cuben Fiber Corporation and North Sails were in competition, North made paneled laminate sails in which a tape of Kevlar, Vectran, UHMWPE, PBO, or carbon would be laid across the joined panels, radiating outward from the corners. I think these tapes were just bonded down onto the surface of the laminate, on top of the film. A similar method might make for a good tarp experiment, I thought.

I purchased some Vectran HT tow (an untwisted, parallel bundle of fibers) on Ebay. It has a breaking strength of about 130 lbs and has about the same thickness as lightweight braided fishing line. I chose Vectran instead of UHMWPE (spectra or dyneema) for two reasons: I don’t want it to elongate (creep) under the constant load of a taught tarp, and individual Vectran fibers have high surface energy and a flattened, tape-like cross-section, which in combination means excellent adhesion to glues.

Vectran is very sensitive to UV, however. The laminating adhesive used by Cubic Tech is also sensitive to UV, and they protect it by mixing in a small amount of finely powdered titanium dioxide. I decided to do the same. So, I bought some nanoparticle (10-30 nm particle size) 99.95% rutile titanium dioxide powder, mixed it with Hysol U09-LV, saturated a couple of short lengths of Vectran HT tow, and layed them down on a piece of the CT0.6K.08, clamping it tightly. The result was a piece of cuben reinforced on the diagonal by imperceptibly thin Vectran tapes.



Clamping forced the parallel Vectran fibers to spread out a bit and lay flush against the cuben. The adhesive was pressed into a very thin film tapering to the surface of the cuben along the sides of the tows. The result is that the Vectran tapes are not only extremely flat, but they also have no edges. It is actually difficult to tell whether they are above or below the mylar. I tried to scratch at them with my nails but there is nothing for a sharp edge to catch on. They are completely flush. My plan is to make a geometric pattern on the tarp, passing over the ridgeline seam and connecting all of the tie-out points to all of the others. I also plan to bond a continuous length of tow under the folded-over catenary edges along the periphery of the tarp. I have yet to settle on a design for the tie-outs.

I apologize for the long post. Any feedback is appreciated.

Edited by ckrusor on 10/01/2010 12:49:51 MDT.

Sounds really interesting. Do you plan on doing any controlled experiments to see if your enhancements make a measurable difference in tension? Very interesting ideas...

Don Meredith

lightpack.blogspot.com

Edited by donmeredith on 03/27/2011 06:58:52 MDT.

Agreed, very interesting.


I also find the cubic tech history a bit interesting also, and I'm curious as to why the only stuff we see these days is the width it is, and laminated with mylar.

I read some old information from cubic tech on some random antiquated site when trolling through UHMW information where they noted that they could laminate with anything, and even do custom widths up to 100" or so.

100+" roll widths could mean seamless flat ridged tarps obviously. The mylar laminate seems to be the weak link in the cuben construction, if cost wasn't an issue, why not laminate with UHMWPE film?


Anyway, I'm curious to see your results.

Very cool, and totally hardcore. Way to think outside of the box. So you would run these bonded Vectran lines to be collinear with the forces from the poles and pegs? Like this:



I actually thought of using a guylines bonded to the fabric for something like this setup but never got around to it and wasn't sure it would really work. Now, there is no point as your idea is WAY better so i will live vicariously through you :).

In the picture, is that a single piece of cuben or is the Vectran sandwiched between 2 pieces? It seems it is just one, but how did you clamp it down without having the clamp bond to the fabric?

Also, if this works out for you, you might want to supply Chris Lucas a sample so he can test it in his tensometer. I did a small document on cuben tieout testing (on my website) and I think it nicely showed where the failures were occurring. If I am understanding correctly how you plan to do this, your lines of Vectran will be aligned with the failures I found and no doubt strengthen them. Keep us posted! Nice work, this is great stuff.

Oh, and for the record, I am also a fan of the lighter cuben weights. I have a tarp made of the 0.33 oz/yd cuben and it is holding up well. Wouldn't use it in a severe storm or anything but it has seen some wind and rain - no problems.

I'm happy to snap any test assemblies you send my way in my tensometer.

Awesome, Steve and I were posting at the same time and reading each others mind!

Edited by ChemE on 10/01/2010 15:18:53 MDT.

Nice work. It sounds like you've got some interesting ideas.

My only comment is that 0.51oz cuben (CT1K.08) contains quite a bit more spectra that 0.48oz cuben (CT0.6K.08) for an extremely minor weight difference....maybe 0.2oz different for the whole tarp.

I think lighter weights of cuben can be used in some applications but everything needs to be well designed. There really isn't room for error in the guyouts, ridgeline etc.

Regarding your ridgeline bond, why don't you do both? Overlap the two panels of cuben and use the tape on either side? It seems stronger...

I really like how HMG does it by actually rolling the two panels of cuben together and then bonding that flat (essentially a bonded flat felled seam).

I think that bonding your vectran is a lot of effort for little gain.

I work for North Sails and do a quite a bit MYOG. I am always getting laughed at by our designers when it comes to strengths of materials used in tarps or shelters. I do not think that we could ever truly test these materials in our applications.

But because of the high cost no wants to push the limits of the lightest Cuben in tarps and shelters when they do blow apart.

A for the Vectran is soaks up water like a sponge as any aramid fiber does so be careful. If you are still interested in that method UK Sails used to make an awful product under the mane of "Tape Drive".

But nice job on pushing the boundries of MYOG.

nick

PS never buy any black sail cloth!!! It is usually full of flaws and dyingthe cloth will normally hide them.

Edited by nick_beaudoin on 10/02/2010 02:08:25 MDT.

It does seem like a lot of effort, and cost prohibitive from a business standpoint. However if he's making this tarp for himself and has the spare time to satisfy his curiosity...go for it! and fill us in on the details while you're at it!

I would think if the Vectran is sufficiently impregnated with Hysol, water absorption should be minimal.

Colin, I too am rather curious as to the exact method you're using for clamping the vectran to the cuben (and how you plan to maintain tension over 9ft+ spans). I could see using a small cuben patch working, and if done cleverly you could probably turn that patch into a tieout reinforcement all in one go without worry of bonding to the clamps.

Good luck, and definitely keep us posted on the experiment, I'm sure there's a few of us who are really interested.

Thanks for all the feedback. Steve, your diagram illustrates exactly what I had in mind, except I plan to add a tie-out or two along the sides, which would also be connected via reinforcing tows to the other tie-outs (and the points that attach to the poles).

The sample in the photo is just a single layer of cuben with the tows bonded to the surface. To clamp the sample I just squashed it between two smooth oak boards with C-clamps. A piece of LDPE masking plastic over the gluey side prevented any unwanted attachment (no glue will stick to LDPE). I have several 15' pieces of oak moulding and about 65 C-clamps (and plenty of LDPE sheet), so I think this method is easily scalable for fabricating the actual tarp.

Thanks for the offer to test a sample, Chris. I'm pretty busy working on my dissertation right now, but I'll see if I can put together a collection of samples to send to you.

Dan, I agree with you about the 0.48oz vs. the 0.51oz styles. I actually had an interest in another product but after a long wait Chris at Cubic Tech offered me the "black" 0.48oz stuff at a (very slight) discount, so I decided to see what I could do with it.

I think that the sandwich-style seam might be the strongest possible seam for cuben. I don't think elaborations on it (like overlapping the panels a bit, etc.) improve the strength. In shear, the bond is already stronger than the mylar. The only reason that the sandwich seam improves upon the conventional single-overlap seam is that it distributes the load across four separate pieces of mylar, rather than two. In figure #2, below, all three of the seams shown should have approximately equal strength, and the more elaborate second and third designs only add complexity and weight. I also think that a bonded "flat-felled seam" is unwise. The bonds at points "a" and "b", in figure #1 below, are in peel when the seam is stressed. Pulling outward on the joined panels would cause the seam to pop open, I think, leaving only a (fairly strong) conventional overlapping bond.



Nick, thanks for the insider tip about the dyed sail materials. Luckily, this lightweight cuben is transparent enough so I can hold it up to a light and look for any major flaws that would affect my application. I'm not sure I understand your concern about water absorbtion. Vectran is not a para-aramid (like Kevlar, Technora, Twaron, etc.) and it has very low water absorption. Published data from several sources reports a value less than 0.1% by mass, whereas Kevlar 49 absorbs 2% and Kevlar 29 absorbs 7%. Also, as Dustin observed, it will be completely encased in cured urethane.

Thanks again for all the feedback. Any input is welcome.

This is an interesting project, Colin, and I look forward to seeing where it goes.

It seems like the advantage of the sandwich bond over the overlapping bond would be nil if the bond is at least as strong as the material. But if not, the sandwich will have double the bond strength. Given that, this hybrid seems like it would be simpler to make and have equal strength to the sandwich (double the bond strength):


------------------
        -----------------------
    ----------

(Hopefully this ASCII art comes through and makes sense - I just mean to tape over one side of an overlapping seam.)

For that matter, it now occurs to me, just doubling the amount of overlap for a simple overlapping bond would have the same effect as well.

That said, I'm probably missing something.

Edited by efredricksen on 10/02/2010 12:50:31 MDT.

"It seems like the advantage of the sandwich bond over the overlapping bond would be nil if the bond is at least as strong as the material."

This is not the case at all. It is BECAUSE the hysol bond is stronger than the mylar that the sandwich seam has an advantage. Two pieces of mylar must be broken (and two mylar/spectra bonds) to pull apart the sandwich seam. Only one sheet of mylar must be torn (and one mylar/spectra bond broken) to pull apart your "open face sandwich" seam or a conventional overlapping seam.

In the figure below, all of the black seams should have approximately the same breaking strength. The mylar must only be torn once, at the red arrow, to break any of the black seams. Stacking on extra layers does nothing for the strength of the seam. Once the mylar has torn, it will readily delaminate to the edge. There should never be a case in which the mylar tears but the seam remains intact, because the tensile strength of the mylar is greater than the shear strength of the mylar/spectra bond over the small area of a seam (very wide seams would be an exception to this). The green seams at the bottom should be about twice as strong as the black seams. But again, the more complex green seams are no better than the simple sandwich. To break these, two sheets of mylar and two mylar/spectra interfaces must be broken at the same time, at the blue arrows.



The hypothesis that the mylar/mylar hysol bond is stronger than the tensile strength of the mylar or the mylar/spectra bond strength has been supported by those who have tested conventional overlapping bonded seams. Failure tends to occur by way of a tear in the mylar followed by immediate delamination or fiber pull-out, not disruption of the hysol bond or clean breakage of the fibers. The mylar/spectra bond is strong enough in shear to transfer the tensile load on the cuben to the spectra reinforcement over a whole piece of material (an area much larger than the interface at a seam), but not strong enough to prevent delamination of the mylar or fiber pull-out once it is torn near the edge (the mylar/spectra interfacial area available to provide shear strength in a seam is very small compared to the mylar/spectra interface across a large sheet of cuben).

Edited by ckrusor on 10/02/2010 20:55:11 MDT.

"Dan, I agree with you about the 0.48oz vs. the 0.51oz styles. I actually had an interest in another product but after a long wait Chris at Cubic Tech offered me the "black" 0.48oz stuff at a (very slight) discount, so I decided to see what I could do with it."

Oh yeah...I think we had this conversation before in another thread.

Good points about the bonded flat felled seam being somewhat in peel. I don't think the HMG ridgeline seem is simply that but it's hard to say. Their site says:

"our tarp ridgeline seams involve a multi-step bonding process, with multiple tapes, creating a ridgeline that is stronger than the fabric itself. This allows the opportunity for a tightly pitched tarp capable to withstand high winds, or even snow. We also employ flat taped seams, stitched seams, and combination seams depending on the seam application"

Here's a pic:

Edited by dandydan on 10/03/2010 02:57:46 MDT.

I'm with you guys regarding the flat felled seam. It would unravel until it became a simple overlap so probably best to avoid it. I like Colins idea with the additional piece of cuben bonded over the seam on the top and bottom. The theory of why it will work makes sense to me, so I am curious as to how it works out. Keep us posted.

Thanks for explaining, Colin. That makes a lot of sense.

Colin, I don't know if you knew that more testing has been done on Vectran and apparently UV degradation tapers off after 400 hrs of exposure, whereas spectra and others continue to degrade as time goes on.

Granted this testing was done on rope, not a tape like you have so it's probably still wise to use the titanium. Do you have any more knowledge on this? Does Vectran create a UV resistant film as it degrades, much like titanium creates a thin oxide coating to protect deeper corrosion?

EDIT: Nevermind, answered my own question. Apparently single fibers continue to degrade with time, meaning that UV penetration is much less than 1/8" (probably .01" to .02"). This is still far too much for the said application so some form of UV protection will be needed regardless.

Data based off:
http://www.vectranfiber.com/BrochureProductInformation/UVResistance.aspx

Edited by upalachango on 10/28/2010 00:38:44 MDT.

Put the Vectran on the bottom side of the tarp, then the tarp would provide UV resistance?

It would work for a pitched tarp and direct sunlight. However not coating it still leaves it exposed to any reflected UV light off rocks and snow or while attached outside your pack to allow it dry/not wet gear inside.

Mixing titanium with the hysol is small (probably messy) step but provides significantly more insurance against possible degradation and minimizes babying of your gear.

Personally I'm a fan of NOT babying gear. I believe well designed gear is created for a particular situation and it should live up to expected punishment of that situation. Accidents and gross negligence shouldn't be factored, but common environmental factors should. Tripping over a guy line or a hungry bear are perfectly acceptable tarp failures. Sunlight and high winds not so much.

I would agree with you , Dustin. On hot afternoons I'd like to have the option to pitch the tarp and throw a space blanket over it for shade, and I don't want to worry about excessive degradation of the reinforcement in places where it is exposed to the sun.

UV protection turned out to be a bit more complicated than I imagined when I decided to look into it. Titanium dioxide is available in several crystal forms (rutile, anatase, brookite, etc.). The cheapest and most commmon form, anatase, tends to catalyze the formation of hydroxyl radicals in large amounts if exposed to water and sunlight. One study investigated a case in which an experimental aircraft had mysterious handprint-shaped areas of paint degradation on it's surface, and anatase-containing sunscreen residue on the hands of the pilot was found to be the culprit. Hydroxyl radicals formed by the anatase TiO2 in the sunscreen destroyed the paint. Another study found that rutile titanium dioxide provided excellent protection against UV damage to plastics, while anatase titanium dioxide radically accelerated photodamage.

Particle size is also significant. More finely powdered titanium dioxide is less disruptive to the adhesive properties of the bonding agent and more opaque to UV (for reasons I don't really understand).

So, I finally found (and not cheaply) nanoparticle rutile Ti02. It tends to cake, and mixing it into the hysol is a pain. I measure out the two parts of the hysol into two separate, chilled ceramic bowls, and mix the rutile Ti02 powder into just one of them, so the mixing time doesn't eat up the hysol curing time. I then mix the two parts of the hysol and apply to the Vectran.

Are you worried about nano particle TiO2?

This is a fairly new form so we don't have a lot of experience with it.

Possibly, if inhaled, it may damage the lungs.

Limited studies say this isn't a problem, but the studies were financed by nano particle manufacturers so possibly they aren't objective.

When you're handling the powder, you might want to try to not breath it. Masks might not be effective because of the small size.