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adatesman
Trad climber
philadelphia, pa
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Topic Author's Original Post - Mar 30, 2008 - 08:02pm PT
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Someone on rockclimbing.com asked about failure modes of SMC's rappel ring this afternoon, and since I was bored I dug one out of the gear closet and threw it on the pull tester. Figured people here might find the results interesting, so here you go.
The setup was a loop of static line (I forget the diameter at the moment... probably 1/2") tied with a water knot at the top and a loop of 1" webbing at the bottom (also tied with a water knot). Both loops were pre-stretched to ~2000 pounds prior to the test to tighten the knots.
600lb-force (2.7kN): ring was still fairly circular
1,000lb-force (4.4kN): ring was rather oval
1,600lb-force (7.1kN): ring was decidedly straight-sided
2,872lb-force (12.8kN): *BANG!!!!*
There was no damage to the static line during the test. The webbing started to be cut by the ring as it approached failure (you can hear strands popping in the video). I should have marked which end of the ring was on the static line and which was on the webbing, but it didn't occur to me at the time. I suspect that the break was on the webbing side though, as the curve on the unbroken side matches up to the static line nicely. The broken side has a much tighter curve to it, which would fit with the webbing allowing it to bend to a tighter radius.
SMC quotes a breaking strength of 14kN. That's only a difference of 275lb-force from the 2872 I measured, so possibly there's some calibration error on my load cell or it was a legitimately under-spec ring (12.8kN is still _WAY_ in excess of anything I'd put on it rapping, so I don't see it as a problem). It could also be that the ring was damaged somewhat by a year bouncing around on my bail biner (not to mention rock...) and getting scratched up a fair amount.
Video of the test
Ring after test:
Webbing after test:
Rope after test:
I like breaking things, so if anyone has any retired or booty gear they'd like to see broken send it my way and I'll post results and video. There's also a testing jig for doing cams in a simulated crack, so that's possible as well. Drop me an email at pulltesting (at) shariconglobal (dot) com if you've got something you'd like broken and we'll make arrangements. Or if you'd like to proof test your Aliens to a certain load that can be done as well.
-aric.
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Raydog
Trad climber
Boulder Colorado
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Mar 30, 2008 - 08:13pm PT
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RE:
"I like breaking things"
cool - thanks.
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paganmonkeyboy
climber
mars...it's near nevada...
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Mar 30, 2008 - 08:26pm PT
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sweet - i like seeing destructive tests that actually come close to the rated strengths of things...
those al rap rings always sketch me out for some reason...
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climbrunride
Trad climber
Durango, CO
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Mar 30, 2008 - 08:30pm PT
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Cool video and great info. Thanks.
I just jumared and rapped off one yesterday. It worked just fine.
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ec
climber
ca
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Mar 30, 2008 - 08:51pm PT
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I always use two...unless desperate, well then one really should use two.
 ec
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marky
climber
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Mar 30, 2008 - 08:53pm PT
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eh, I don't care if maybe it holds 2,000 lb, or maybe not
just as long as it CERTAINLY holds 164 lb
thanks for the info, which is informative
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Raydog
Trad climber
Boulder Colorado
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Mar 30, 2008 - 09:00pm PT
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kinda interesting thing to do which a lot of climbers know
get on a basic home (analog*) scale and without
leaving the "ground", un-weight, then use
downward inertia to "load" the scale...
at 133 lbs I can generate a 500 lb load pretty easy
* maybe a digi would work too
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Chaz
Trad climber
So. Cal.
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Mar 30, 2008 - 09:49pm PT
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One ton aprox. = about what I would have guessed they're good for.
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Majid_S
Mountain climber
Bay Area
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Mar 30, 2008 - 11:40pm PT
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What was your load cell readout before you break the ring ? 2800 lbs ?
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fear
Ice climber
hartford, ct
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Mar 30, 2008 - 11:52pm PT
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FWIW I pull tested a bunch of those a year ago and got over 2000 pounds even on ones that were significantly worn and probably 10 years old. Every single one deformed just like that picture above before they broke.
But I still like to use 2 as well.
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Ed Hartouni
Trad climber
Livermore, CA
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Mar 31, 2008 - 01:06am PT
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cool,
I've been using the Omega Pacific ring lately, it's solid, and really beefy, with a 20kN breaking strength.
I usually only use one of these, overkill strength, won't wear through like the tube ones. About the same price..
http://www.omegapac.com/product180.html
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Clint Cummins
Trad climber
SF Bay area, CA
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Mar 31, 2008 - 05:47am PT
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Ed,
I added an SMC ring to your Omega on the tree on the alternative rappel from Dream Easy! Also a second sling! (Just trying to thin down my huge collection that I have lifted from other routes - I have never bought rings and have not bought slings in decades....)
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MisterE
Social climber
My Inner Nut
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Mar 31, 2008 - 09:42am PT
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I was always a bit sketched out by the hollowness of those rings as well, until I crush-tested one in a vice about 10 years ago. I had to get a 4-foot extension bar before it even bent. End of worries!
Thanks for posting that. Erik
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adatesman
Trad climber
philadelphia, pa
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Topic Author's Reply - Mar 31, 2008 - 10:41am PT
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Raydog-
Playing around with the load cell while bounce testing, I think we were able to get 5 or 6kN. So yeah, its quite possible to put much more than body weight on these things in normal use.
Stich-
Yeah, I was rather surprised by how the chain unraveled. Didn't think it would do that. I was bored enough to cobble together a way to make it work, but not bored enough to drag the puller outside to weld on a bracket on top for the hook and eliminate the chain. Its on the short list now though.... Plus I think the video software I found can do picture in picture, so chances are I'll see about getting my hands on another webcam and move the readout well out of harms way. That said, a bunch of plexi wouldn't be a bad idea anyway....
Majid-
The readout was set to show the peak force applied, so the 2872 displayed at the end was the point where it broke. FYI, the last stroke on the pump was relatively soft and gave little increase in the applied load, so my guess is that failure came from the tube collapsing.
-aric.
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Jingy
Social climber
Flatland, Ca
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Mar 31, 2008 - 10:46am PT
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Sounds like a test for Russ Walling!
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WBraun
climber
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Mar 31, 2008 - 11:12am PT
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adatesman
What load cell are you using?
Who's the manufacturer of your display? My display is a Transducer Technigues DPM-3.
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nature
climber
Santa Fe, NM
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Mar 31, 2008 - 11:14am PT
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He's probably already been there and done that.
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adatesman
Trad climber
philadelphia, pa
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Topic Author's Reply - Mar 31, 2008 - 12:19pm PT
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WBraun-
If you're interested, there's a write-up about the rig over at rockclimbing.com with all the details, but the quick version is that the load cell is a 10k-lb unit from Transducer Technologies and the strain gage indicator is a Daytronic 4077.
I went with the Daytronic because the 4077 has an completely analog peak capture channel, which avoids the issues with scan rates when doing drop tests. Then again, I think the scan rate is something like 1000 samples per second, so it might not be that big an issue.
The data sheet for your DPM-3 says it has a peak capture.... Happen to know if that peak capture is separate from its normal 60 samples per second scan rate? Looks like a nice unit. I probably would have ended up with something similar had I not found a deal on a pair of the Daytronic ones on Ebay.
-aric.
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WBraun
climber
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Mar 31, 2008 - 12:38pm PT
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Thanks aric
I got my DPM-3 on eBay also including my load cell, 10,000 pound S type.
Your Daytronic 4077 is unreal expensive new. I hope you scored a killer deal.
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adatesman
Trad climber
philadelphia, pa
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Topic Author's Reply - Mar 31, 2008 - 01:32pm PT
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WBraun-
No joke... They're wicked spendy. The auction I found was poorly listed and I ended up getting a pair of them for something like $250. :-)
-aric.
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