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scott0708
Nov 18, 2007, 9:48 PM
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So, I got my hands on some rope that my gym was retiring and thought I’d have some fun with it. I was supposed to go climbing down at the RRG this weekend, but my partner got sick, so I have a little free time. In the name of science, I will attempt to test some rope to failure.
Rope info: I don’t know too much about it. It looks to be about 11mm, and as been used for over a year for both TR and leading (all indoors).
The setup: One end of the rope is secured to a solid branch 15’ off the ground. It is secured with a number of wraps around the branch. There is 12’ of rope between the branch and the test weight, which consists of 2 25 lbs iron plate weights. The weights are tied in with a figure eight directly through the holes in the middle of the weights.
There is a separate rope used to hoist the weight into place. This rope is rigged through a caribiner roughly 30’ off the ground, enabling us to hoist the test weight 27’ off the ground (the full length of the test rope).
Procedure: We hoist the test weight up and then release the hoisting rope, allowing the test weight to fall.
Results: for the first 2 tries, we hoisted the test weight even with the test rope’s anchor, 15’ off the ground. This produced a FF1. The rope survived.
Next, we upped the drop height to 27’, making for a FF2. We did 10 drops from this height, and observed no noticeable damage to the rope. The test weight was not hitting the ground, so all of the force was being caught by the test rope.
At this point, we were getting bored, and so decided to add more weight. We added two 20lbs dumbbells, girth hitch with a nylon sling. The sling was then clipped to an overhand knot we tied above the other two weights.
The dark blue rope is the test rope and the light blue rope is the hoisting rope.
With the new test weight of 90 lbs, we conducted three tests all from 27’ (FF2). Hoisting this weight into place was very difficult, and I had to break out my jumars to enable us to haul the rope.
The rope survived all three tests without visible damage. At this point, however, the rope felt like a steel cable and had very little stretch. In first few tests, the weights bounced quite a bit, but now there was little elasticity left in the rope. Also, I undid the test rope from the branch. I observed a hard black glaze where it had been wrapped around the branch. I guess the rope slipped a little during the first few tests as the wraps tightened around the branch.
At this point, we decided to conduct a side test with another length of retired rope. We suspended the test rope and attached the 90lbs worth of weights to the end. Then, using 3mm diameter cord, I attempted to saw through the test rope. I had read at http://www.psychovertical.com/?avoidingthevoid that it was very easy to cut through a rope that was under tension by melting it (the friction from the nylon on nylon contact). This website says that it will take about 2 seconds. Anyways, it took much longer. After about 1 minute, there was a noticeable glaze on the sheath. Another 2 minutes melted through the sheath and exposed the core. Another few minutes cut through most of the core strands. Eventually we did cut all the way through, but all told it took around 6 minutes of hard work and my arms were very sore.
Conclusion: while nylon on nylon friction is clearly very dangerous, it is not really an easy way to cut a rope. I guess it might come in handy in a rescue situation, but it is fairly impractical, as the rope has to be under tension and it takes several minutes of hard work. Always carry a knife.
Back to the original drop test, we continued to use a 90 lbs test weight, but we rigged a better system to hoist the weight up (a 2:1 advantage). Using this rig, we did 7 more drops, all FF2, and the rope did not break. We did, however, have a biner fail. The biner that was connecting the 2 20 lbs dumbbells to a knotted loop in the test rope snapped in half.
The biner that would fail
The failure was very violent, and it sent the upper half of the caribiner flying all the way over the house, landing about 100’ away.
Since the gate shows no signs of damage, we speculate the gate was somehow pinned open during the fall. Alternatively, the gate could have lashed open at the moment of impact. This particular biner has an open gate rated strength of 7kn. The Biner is stamped “ACE” and it came free with a Rock Empire Cam I ordered from Pagangear.com. One interesting thing is that this biner was only attached to 40lbs and still exceeded 7kn, meaning the entire test weight (90lbs) probably generated twice that.
The sharp edges from the biner failure also appears to have partially cut through the sling that was holding the dumbbells. I will continue to use the sling in tests and see if it fails.
Anyways, I ran out of time today to continue the tests. I have left the rig up outside and will hopefully have time in the next few days to finish the tests (break the rope!).
Conclusions so far: Ropes are pretty strong, biners can break if the gates are open.
If anyone has any suggestions, questions, or ideas for more tests (I have some more retired rope), I’d love to hear them.
Thank,
Scott
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cantbuymefriends
Nov 18, 2007, 10:35 PM
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I'm impressed by your work 
Did you notice/measure any difference in "free-hanging" length (with the weights/dumbells) of the rope between the drops? I.e. it would've been interested to see how much of the stretch that would remain until the next test.
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scott0708
Nov 18, 2007, 11:12 PM
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Thanks
I didn't actually measure the amount of rope stretch between drops, but I did notice that the rope stretched. After the first few drops, the weights were hanging a full foot lower, but this may have been due to rope slipping around the tree branch.
Later in testing, the weights began to hit the ground, meaning the rope had stretched even more. At this point the wraps around the branch were very tight, so I don't think this was due to rope slippage.
When I do some more tests, I'll try to measure the rope stretch specifically.
-Scott
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el_layclimber
Nov 18, 2007, 11:13 PM
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Interesting to see a biner fail at what must be a pretty low impact force. I believe that recommendations on retiring ropes are not because they are going to break, but because they lose their dynamic properties over time. Too bad you have no way to measure rope stretch, especially compared to a new section.
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ja1484
Nov 18, 2007, 11:15 PM
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Uh, well done I guess, but not much there that wasn't already generally known.
As for the biner - yikes. I suspect it's a combination of loss of elasticity in the rope, and open gate issues.
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scott0708
Nov 19, 2007, 12:10 AM
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Yeah, I realize there's nothing too groundbreaking about the tests, I was just out to have some fun.
The test was by no means scientific, so take it as you will.
That's a good point about the rope losing elasticity as it ages and sustains more and more falls; definitely a good reason to retire older ropes.
I also was surprised that the biner failed, but I guess the lack of stretch made fall relatively static. That, or the biner was bad to begin with. I had never climbed on that biner before, despite the fact that it was stamped "CE".
-Scott
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ja1484
Nov 19, 2007, 12:14 AM
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scott0708 wrote: I also was surprised that the biner failed, but I guess the lack of stretch made fall relatively static. .
That's my primary suspect - due to both age and the fact that several drops had occurred prior to the failure, and the rope was stiffening. Recall that in UIAA drop tests, the rope is not allowed to recover its elasticity between drops. Hence impact force rises as the test goes on, eventually rising enough to snap the rope.
But, of course, this doesn't occur in the real world, so it's not a concern we need have.
But I think that's what happened in this case - a combination of static loading (and impact forces on static materials have been shown to be NASTY high in some work PMI did several years back) and gate lash.
(This post was edited by ja1484 on Nov 19, 2007, 12:15 AM)
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maldaly
Nov 19, 2007, 12:42 AM
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scott,
There are two things going on here that I'm not sure you're giving credit to. First, unless I mis-read your procedure, the hauling rope is still running through the top carabiner when you drop it. Is that the case or do you have some kind of release? If the rope is running through that top carabiner, that seemingly little amount of friction will absorb a lot of the energy of the fall. People have survived 120' ground falls when their rope was running through the top anchor but not belayed.
Second, you're only using 90 lbs as your load. The UIAA/CE tests call for 80kG or about 176 lbs. I can't do the math but I'll bet that that the amount of force generate by a 27' fall with 90 lbs vs 180 lbs is roughly half. Combine the two and I'll bet that you're not actually generating as much force as you think you are. It would be interesting to put a load cell at the falling mass to see what's really going on.
An official UIAA/CE drop is an incredible violent affair. Witness one and you'll make sure that you never set yourself up for one, I promise.
Climb safe,
Mal
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scott0708
Nov 19, 2007, 1:28 AM
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Mal-
Thanks for the response. That’s crazy to hear about the amount of friction from the top anchor. In our first ten tests, when we were just dropping 50lbs, we simply let go of the hoisting rope, so there would indeed have been some friction, but we didn’t really notice it.
When we added the next 40 lbs for the last 7 tests, we rigged a 2:1 hauling system. With this, we needed to improvise a quick release system for exactly the reason you mention.
Once the test weight was hoisted into place, it was transferred directly onto a small loop of 3mm cord. To perform the drop, we would simply cut the small loop of cord and then replace it for the next test. I hope that all makes sense.
As for the test weight, I do realize that 90lbs is unrealistically low, but that’s all I happened to have. Also, it was pretty tough to raise the weight as it was. If I get the time and do some more tests, I’ll try to find more weights.
-Scott
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maldaly
Nov 19, 2007, 1:40 AM
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Sounds like you've got the right idea. We like to use a haulbag full of sand and, yeah, getting it up is a PITA. When Petzl does their drops they use a winch powered by a car battery.
The 3mm works okay but I hate being underneath 80kG held by a shoelace. If you've got the $ try this: http://www.kitesurfari.com/store/wichard.html
it's got lots of other uses as well.
Mal
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curt
Nov 19, 2007, 4:41 AM
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I'll second what Mal has said. This testing may be comforting news for all of the 90 lb. climbers out there--but it doesn't mean much more.
Curt
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scott0708
Nov 21, 2007, 5:03 AM
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Ok, so I had some more time today, and I decided to do some more testing. In order to make the tests a bit more realistic, I wanted to up the test weight. I took an old paint bucket and reinforced it with some webbing and duct tape, and then stuffed it full of rocks. It weighed 62 lbs.
So, with all the other weights, the total tests weight is now 152 lbs, almost exactly my own weight.
Other than the additional weight, the tests were conducted the same as before: the test weight is suspended by about 12’ of rope. It is raised up used a second rope and a 2:1 pulley system. Once the test weight is at the top, it is transferred to a small loop of 3mm cords, which we cut to release the weights.
My low-tech quick release system
With the new 150 lb weight, we conducted 7 drops, and the rope showed no visible damage. After all of these drops, plus the many drops the other day, the rope had lost nearly all of its elasticity, which led to another carabiner failure.
This one was similar, though not nearly as violent, as the one in the original test. It appears to have been an open gate failure, in which the gate was either pinned open or lashed open at the moment of impact. The nose of the biner bent upwards, allowing the gate to spring outwards. As the load bounced up and the biner was momentarily unweighted, the nose of the biner flexed back into place, leaving the gate stranded on the wrong side of the nose.
This is just my interpretation anyways; I’d love to hear if anyone else thinks this is plausible or has an alternate theory.
On other possibility is that the gate was bent sideways around the nose of the biner. This does not seem likely to me, as it does not move side-to-side at all, and there is no visible damage to the gate’s hinge.
One somewhat disturbing thing to note is that this biner was the exact same brand (Ace) and model as the one that failed in the original tests, although this was straight gate and the other was bent gate. Those were my only two biners from this company, and I guess I won’t be getting any more.
So, after the 7 drops with the 150 weight, the side of the paint bucket burst open. So I decided to continue with a few more drops with the remaining 90 lbs. I did 6 more drops with this weight, and observed no further damage.
Conclusions:
To total it all up, the rope has survived 2 FF1 drops with 50lbs, 10 FF2 drops with 50 lbs, 16 FF2 drops with 90 lbs, and 7 FF2 drops with 152 lbs, not to mention over a year of hard use both TR and leading in a gym. The rope is still going strong, although is declining elasticity is very apparent, and probably contributed to the failure of the biner and the paint bucket.
I’d really love to have the rope fail, but I guess I’ll have to round up some more iron weights.
-Scott
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billcoe_
Nov 21, 2007, 5:39 AM
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Is that a Lone Wolf double action? Didn't know that they made that knife with the partial serrated blade.
Anyhow: the Ace failure surprised me. It was one of the reasons I went to these beauties: 10kn gate open strength.
Any chance you could drop test a few biners?
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scott0708
Nov 21, 2007, 6:37 AM
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The knife in the pic is a Gerber fastdraw (great knife).
Good point about the biners, I too look for quality brand name biners with high open gate strength (although I don't have any heliums).
I am definitely intrigued by the biner failures. I don’t know too much about calculating fall forces, so I used petzl fall simulator (http://en.petzl.com/...l=56&Activite=14) to try to do some calculations. As I said before, both biners that failed were clipped only to the 2 20lbs dumbbells, and so should have held only 40lbs. Using the fall simulator, a 40lbs “climber” taking a 8m factor 2 fall on “11mm UIAA rope” should generate 5.8Kn. I selected grigri as the belay method, since I guess this is the most static. The “belay” in the case of my test was completely static, so this probably increased the forces somewhat. Would it have increased the forces to over 7kn, the point at which the biners should have failed open gate?
Now, one important thing about my test was that the rope had endured many consecutive high impact falls, which greatly reduced its elasticity. If I re-run the petzl fall simulator using static rope, the force increases to 8.3Kn, above the biner's rated strength of 7kn.
I suspect the rope used in the test was somewhere in between the 11mm rope and the static rope in terms of elasticity.
So, I guess it is not unreasonable that the biners failed. Having said that, it does strike me as odd that both of the Ace biners failed while none of the other biners I was using showed any damage. I guess I would not recommend using Ace biners to any of my friends.
Also, this test reinforced in my mind the advantage of wiregate biners. It is very likely that one or both of the failed biners suffered from gate lash, and wiregate are not nearly as susceptible to this. Also always make sure biner gates are not pinned open against anything.
As for drop-testing biners, this is something that I'd like to do, and I have a few old/bootied biners lying around. I'm not sure how useful my results would be, as I really can't determine the actual forces generated in the tests. I will probably try some though, if only for the fun of watching biners explode .
-Scott
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j_ung
Nov 22, 2007, 3:49 PM
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In reply to: Conclusion: while nylon on nylon friction is clearly very dangerous, it is not really an easy way to cut a rope. I guess it might come in handy in a rescue situation, but it is fairly impractical, as the rope has to be under tension and it takes several minutes of hard work. Always carry a knife.
Looks like a fun way to spend the afternoon! But, you shouldn't trust your conclusions entirely.
The above conclusion is especially (shockingly) inaccurate to me. I've seen it happen in, I'm guessing, about three seconds. And I suspect that, if you load nylon running over nylon in an actual fall, the stationary cord will break pretty much instantly. I think the reason why it took you so long is because the test was flawed. The hanging rope was free to swing toward the sawing cord. Try it again, but this time, have another person hold both ends of the thick rope while you saw the thin cord across it. If both of you pull as hard as you can while doing this, the rope will separate much sooner, and you will not have even approached the tension and friction you can achieve in fall conditions.
Fun thread.
(This post was edited by j_ung on Nov 22, 2007, 3:53 PM)
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scott0708
Nov 24, 2007, 4:41 AM
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j_ung-
Thanks for the comments, I've definitely had fun messing around with this stuff!
I think, however, that either you misunderstood my conclusions, or I didn't understand your comment. My point was not that nylon running over nylon could not cut a rope; it certainly can. As you point out, in a fall situation the rope could be cut much more quickly. Also, in my test I was trying to cut the rope clear through with the cord. In a fall situation, even a small amount of cutting could weaken the rope to the point of failure.
As I'm sure you know, many speculate that this was the cause of the rope failure in Dan Osman's death.
My experiment was to test whether or not using thin cord to purposely cut a rope was practical in emergency situations (if you dropped your knife). My conclusion was that, while possible, it was more difficult and time-consuming than I had thought.
As Skinner pointed out, I should re-do the test with 2mm cord and with the rope under full body weight (in the first test I used 3mm cord and the rope was only holding 90 lbs). I will do this in the next few days and report back with the results.
On a related note, when I was trying to think of more ideas for testing the rope, I did try to come up a test that would simulate what j_ung was referring to: the rope being cut by nylon-on-nylon friction during an actual fall. Maybe a setup where the test rope would fall over another rope strung horizontally? Maybe if the "cutting" rope were strung diagonally, the test rope would slide along it while falling?
Anyways, with a good setup and come luck I might be able to recreate the "Osman" scenario and cut a rope on another rope during a fall.
Skinner: Yes, a high-speed camera would certainly be awesome. Here's one: http://www.visionresearch.com/...files&page=miro1. I tend to be wary of anything where you have to "request a quote" though . Hmm, Christmas is pretty soon...
You're right about the rope-cutting test, I tried using 1 and 2 wraps of 3mm cord around the rope. Using just 1 wrap seemed to be the most effective. As I said, I will re-do the test with smaller cord and bigger load and see what happens.
USNAvy: Thanks for the comments. I too am interested in testing other biners, including some "better" brands. Of course, it is impossible for me to create ideal, repeatable testing conditions, so my result wouldn't really have any scientific value, but it'd be fun to do.
Thanks everyone for the comments and the interest. Yes, I've definitely had fun playing around with this stuff. I guess this is what a climber in Michigan has to do to entertain himself .
-Scott
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antiqued
Nov 27, 2007, 3:01 AM
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Thanks for the effort and the reports. I have a suspicion about the broken biners - the first one you show
looks to me like it could easily be opened at the onset of 'impact' by the rope down to the weight discs. That is if the rope floats a little during the free drop. Was the second biner to break postioned so that might happen to it also? (Although it might have 'captured' the strand)
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scott0708
Nov 30, 2007, 4:45 AM
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In reply to: Was the second biner to break postioned so that might happen to it also? (Although it might have 'captured' the strand)
Yes, the second biner to fail was in the same spot as the first. I agree that it was an open gate failure, either due to "gate flutter" or the gate simply being pinned open.
-Scott
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scott0708
Nov 30, 2007, 5:05 AM
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OK- so I've had a chance to conduct another test, re-doing my earlier attempt at cutting a rope with thin cord. In my earlier attempt, I used 3mm cord and the rope weighted with 90 lbs, and it took 6 minutes of hard work to cut all the way through. I concluded that purposely using cord to saw through a rope was not really that easy.
Anyways, it was suggested that I re-do the test with two changes: thinner cord (2mm) and full body-weight on the rope.
So I went to the local REI, and they didn't have any 2mm cord. So I got the thinnest cord I could find: Kevlar shoes laces (http://www.rei.com/...2159?vcat=REI_SEARCH. These are for Salomon shoes, the fancy kind with quick-fitting laces, and they are quite skinny, probably between 1 and 2 mm.
For this test, I hung from the rope, in my harness, about a foot off the ground. I wrapped the kevlar cord once around the rope and used a back-and-forth sawing motion. The rope was cut through in JUST 8 SECONDS! This was amazing to me, and was so different from the previous test.
The cut rope, kevlar cord, and a biner for size reference.
So, the new conclusion: It is definitely possible to cut through rope with a smaller cord, and with a small enough cord and enough weight on the rope, it can be accomplished very quickly. I'm still not sure how practical it is, since I doubt many climbers typically carry around cord this thin. Seriously, even normal shoe laces are more than 3mm. I guess if your wearing Salomon shoes, you'll be alright.
Alright, I still do want to carry out more drop tests on my rope, but at the moment I'm hampered by the frigid Michigan weather (I did the rope-cutting test in a gym, but I don't think they'd be happy with me doing drop tests there).
-Scott
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caughtinside
Nov 30, 2007, 5:15 AM
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breaking shit is fun.
thanks for posting, I enjoyed reading it.
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