Opinions on 6mm Kevlar Cord

wfscot wrote:Why not just regular old 6mm nylon (perlon)? Single strand breaking strength is over 7kN. In just a simple loop, you're up at 14kN. Two piece pre-equalized anchor = 28kN (less for bad equalization down to 14kN worst-case). Three piece = 42kN (again, down to 14kN). Strong enough for me. Beyond that, it's slightly dynamic, which makes it a lot less likely you'll ever see those forces. And it's cheap. Even for reslinging gear, 14kN is stronger than most gear. What am I missing?

realistically ... a loop is considered conservatively to be 100% of the single strand strength

from mammut ...

It is correct that using a loop increases the strength, and in theory it could even be doubled when compared to the strength of a single strand. The caveat is that in a climbing anchor the strength of this cord loop is never doubled, not even close. As part of discussing this, we did a semi-scientific experiment to illustrate the point. We took a loop of 7mm nylon cord (13kn tested breaking strength) and tied it into a loop with a double fishermans knot. When clipped into a carabiner at each end and pull-tested, this broke at the carabiner (picture 1) at roughly 35% higher load than the stated cord strength—not double, but still significant.

HOWEVER, when you pull test like this it is important to remember that the carabiners and knots are the weak links, and changing those will dramatically affect the ultimate strength—it is hard to believe how much variability there is in this when you test in slightly different configurations and with different but similar equipment, but as a general rule any carabiner or knot is going to weaken whatever it’s clipped to. Add in a carabiner with a small rope-bearing surface or a sharp edge (like a burr on the inside of the biner from being weighted on a bolt-hanger?) and you further change the equation. In reality, given the vagaries of the above in addition to simple wear and tear, I would be nervous of relying on any one arm of a knotted cordellette anchor to hold too much more of a load than the tested cord strength—I like to plan for worst cases with the assumption that whatever can go wrong probably will at some point (and so far I’ve been right 100% of the time!).


highinfatuation.com/blog/co…

ZOMBAY THREADS !!!

;)

bearbreeder wrote: realistically ... a loop is considered conservatively to be 100% of the single strand strength from mammut ... It is correct that using a loop increases the strength, and in theory it could even be doubled when compared to the strength of a single strand. The caveat is that in a climbing anchor the strength of this cord loop is never doubled, not even close. As part of discussing this, we did a semi-scientific experiment to illustrate the point. We took a loop of 7mm nylon cord (13kn tested breaking strength) and tied it into a loop with a double fishermans knot. When clipped into a carabiner at each end and pull-tested, this broke at the carabiner (picture 1) at roughly 35% higher load than the stated cord strength—not double, but still significant. HOWEVER, when you pull test like this it is important to remember that the carabiners and knots are the weak links, and changing those will dramatically affect the ultimate strength—it is hard to believe how much variability there is in this when you test in slightly different configurations and with different but similar equipment, but as a general rule any carabiner or knot is going to weaken whatever it’s clipped to. Add in a carabiner with a small rope-bearing surface or a sharp edge (like a burr on the inside of the biner from being weighted on a bolt-hanger?) and you further change the equation. In reality, given the vagaries of the above in addition to simple wear and tear, I would be nervous of relying on any one arm of a knotted cordellette anchor to hold too much more of a load than the tested cord strength—I like to plan for worst cases with the assumption that whatever can go wrong probably will at some point (and so far I’ve been right 100% of the time!). highinfatuation.com/blog/co… ZOMBAY THREADS !!! ;)

It depends a lot on the material used. Nylon cord is much more forgiving to knots and being loaded over a narrow diameter (the biner) than low stretch fabrics like Dyneema and Kevlar. Cord also tends to fair much better than webbing over narrow edges.

I havent tested too much cord, but I found that webbing rated for around 18kN will hold about 2300 lbf end to end with over hand knots, and about 22kN when tied in a loop with a water knot. Interestingly, the failure point when loaded in a circle is not the knot but the carabiner. Webbing really doesent like being loaded in a circle. Likewise, if I use a large webbing drum, then I can up the strength to around 28kN for a single loop.

20 kN wrote: It depends a lot on the material used. Nylon cord is much more forgiving to knots and being loaded over a narrow diameter (the biner) than low stretch fabrics like Dyneema and Kevlar. Cord also tends to fair much better than webbing over narrow edges. I havent tested too much cord, but I found that webbing rated for around 18kN will hold about 2300 lbf end to end with over hand knots, and about 22kN when tied in a loop with a water knot. Interestingly, the failure point when loaded in a circle is not the knot but the carabiner. Webbing really doesent like being loaded in a circle. Likewise, if I use a large webbing drum, then I can up the strength to around 28kN for a single loop.

from the DAV ... their test definately shows nylon as generally losing less strength in knots

also from the DAV is their latest timely article on nylon vs dyneema vs kevlar ...

alpenverein.de/chameleon/pu…

interestingly they suggest not to use tied nylon slings either in a loop, but especially not the single nylon 16mm strand finished off with a knot at each end

;)

Oh how I wish the DAV published an English version. So much good info and such poor Google translation. So many good reads from the DAV

mattm wrote:Oh how I wish the DAV published an English version. So much good info and such poor Google translation. So many good reads from the DAV

The DAV membership who pay for the research to be done can generally read German:-)

wfscot wrote:Why not just regular old 6mm nylon (perlon)? Single strand breaking strength is over 7kN. In just a simple loop, you're up at 14kN. Two piece pre-equalized anchor = 28kN (less for bad equalization down to 14kN worst-case). Three piece = 42kN (again, down to 14kN). Strong enough for me. Beyond that, it's slightly dynamic, which makes it a lot less likely you'll ever see those forces. And it's cheap. Even for reslinging gear, 14kN is stronger than most gear. What am I missing?

That accesory cord and tape are tested over large diameter drums to obtain a value for the ultimate strength of the material. Tested over a karabiner or with knots the strength is considerably lower,around 35%-40% less for most.

What about Bluewater 5.5mm titan cord? Ive been using that for a cordlette. Is this a good idea?

Jim Titt wrote: The DAV membership who pay for the research to be done can generally read German:-)

Das ist güt aber mein deutsch ist sehr schlecht. Gäbe es eine Englisch-Version, würde ich für die Mitgliedschaft bezahlen.

My last German lesson was 15 years ago so it's rough going when I try to read the technical stuff the DAV puts out.

Jim Titt wrote: That accesory cord and tape are tested over large diameter drums to obtain a value for the ultimate strength of the material. Tested over a karabiner or with knots the strength is considerably lower,around 35%-40% less for most.

I think they test single strand (no drum/edge involved). I get your point, though. Knots and sharp bends weaken *all* material (tech cord included). In terms of slings, I know tech materials weaken far more than nylon (after learning that, I stopped knotting my tech slings). I don't see why that wouldn't apply to cords, too.

All that said, I'm not sure it really matters. So lets say that simple loop strength is 10kN instead of 14kN. Ok. So two pieces are still in the neighborhood of 20kN (properly equalized). That's still plenty strong, right?

I'm asking in all seriousness, BTW. If I'm risking it by using 6mm perlon for multi-piece anchors, I'd love to get some data so I can change my behavior.

Oops. Responded too fast. I just saw beerbreaders DAV data and links. Thanks!

So, given all that, how do people feel about 6mm perlon cordalettes? Even with the reductions in strength over a biner and at the double fishermans, it still seems strong enough for a multi-piece anchor. Thoughts?

It's amazing how much nicer it is to carry 6mm vs 7mm. If 6mm stops being an option, I'm guessing I'll shell out for tech cord as well.

http://www.edelrid.de/en/Edelrid/Sports/Aramid-Cord-Sling-6mm-night.html?listtype=search&searchparam=aramid

I've been using these for a while now - no problems so far.

wfscot wrote: I think they test single strand (no drum/edge involved).

The proper name is "bollard", and there's a pair of them. They're used because they're the only way to create an attachment that doesn't degrade the ultimate strength of the sample.

theuiaa.org/safety-standard…

Aric Datesman wrote: The proper name is "bollard", and there's a pair of them. They're used because they're the only way to create an attachment that doesn't degrade the ultimate strength of the sample. theuiaa.org/safety-standard…

True, although I have always disagreed with that testing method. Drums are good when conducting R&D, testing different weaving patterns and such. But the problem is that a drum test does not extrapolate to the real world. It's kind of like if IIHS only tested vehicle crash ratings by slamming a car into those sand-filled yellow barricade blockers they put on freeways. That doesent really tell us enough of the story.

The problem is that there are weaknesses that can exist in some designs that do not become apparent in drum testing, but are apparent when the sample is tested over a carabiner. For example, very-low-stretch fibers like aramid and Dyneema fair worse over narrow edges than higher stretch material. This has been somewhat-well documented in webbing testing where nylon webbing typically experiences a modest decrease in strength going from a 4" drum to a 1" drum, but polyester, and especially Kevlar and Vectran webbing, experience a much steeper drop. I have seen tests where polyester webbing had a strength rating of 140%+ of it's nylon counterpart when tested on a drum, but when tied into an overhand knot it was actually weaker than its nylon counterpart.

I believe it might be more beneficial to test webbing and cord the same way the UIAA tests most of its other samples—over a carabiner edge.

It´s one of those yes and no situations. the manufacturers only make and sell a product not an application and so the product itself is tested in a way to accurately reflect the products performance. The moment it becomes an application then the test changes to reflect the performance in that aplication so that tape sold by the metre is tested one way and the same tape sewn in a sling is tested another way.
Since no-one knows what the end user is going to do with the product it is impossible to specify a test other than the one used. It is then the climbers responsibility to either know what the affect of their application is or not use the product ouside it´s recommended use.
Most climbing equipment isn´t in fact tested reflecting a real-life situation since it is usually physically impractical or the results aren´t accurately reproducible.

Technora is used for canyoneering ropes. It's no going to break from repeated flexing.

It was actually designed for the military for rappelling on ultra thin lines. Basically to be carried behind enemy lines where a 70m rope would be a lot of weight.

I don't like it for anchors becsuse it's a bit stiff, knots tend to be hard to untie, and the associated dynamic issues. I do have it on my hexes and my ghetto reslung cams. Works great for that.

Also, sterlings cord only requires a double fisherman's vs a triple for most aramid cords. Less knot bulk.