the Machine that Breaks Things claims some more victims

[frobzwiththingz]

Today we broke some rock climbing slings.



Recently i retired a couple of climbing slings that had been in service at the space where we have our weekly aerials practice group. They are both made by Sterling Ropes, and were the 1/2 inch Spectra "Rabbit Runners". Their stated rating when new is 22 kN (~4900 lb). This is the climbing world, that number is actual breaking strength, (3-sigma method), *not* "working load". They had been in use for about a year and a half, holding up either half a trapeze, or a tissu setup, and used on a weekly basis for a 3-hour practice session. So; roughly 75 practice sessions later, how strong are they now?

The point where the 'biner clipped in looked like this on both of them.
Not too bad, really. Spectra seems to be pretty magical stuff w.r.t abrasion resistance.


So here we are, set up on the Machine That Breaks Things.



I've got both ends rigged up as choker configs, with PVC tubing to protect against the roughness of the eyebolts on the sensor and turnbuckle.




Used in the choker config, conventional wisdom would be to derate the load ratings by 25%. When new, that brings us down to 3675. So that gives me an idea of when to start expecting badness. But will the slings fail at the choker knot, at the place where the biner abrasion was, or somewhere else entirely?

For each sling, i did the following:
1) load the sling slightly (~25 lbs), and adjust the chokers such that the strands were even.
2) take it up to 250 and check evenness again.
3) take it up to 2000lbs. Both slings held. Let them back out.
4) Pull until failure.

The first sling failed at 3816 lbs. It snapped in *two* places:



I suspect that one side gave way first, and the resulting girth hitches around the eyebolts actually resisted slippage, causing the other side to go as well. Without high-speed photography, i'll just have to guess. Surprising thing, though; *neither* of the two failure points was where the 'biner abrasion was. And it didn't break at the chokers. Admittedly, on this sling, there was much less abrasion than on the other one.

The second sling failed at *4430* lbs. Only one failure point this time (slippage at the girth hitch occurred), and it was at the spot where the 'biner abrasion was.



close-up of failure:





Conclusions: These things are still quite strong, even after a lot of use.

Comments

[perspicuity.livejournal.com]

holy crapola :)

i have spectra (and kevlar) kite lines. rated at LEAST in some cases for 300-500 pounds... if they are properly sleeved, at least for my non traction application, over years of use, i've never broken one. so, there's some hope. stuff isn't cheap.

love that machine.

i have to wonder how strong some thing are ... if materials like that sling are that strong... mmm. ponders.

#

[bikergeek.livejournal.com]

The steel company I used to work at did testing of a very similar type. Cut a dogbone-shaped piece of steel out of a plate, put it in a Machine That Breaks Things, pull it like taffy and measure yield and tensile strength.

A36 structural grade steel plate needs a yield strength of 36,000 lbs/in^2 minimum, and a tensile strength of 58,000-80,000 lbs/in^2 depending on thickness.

[whitebird.livejournal.com]

You have all the fun toys!

[sicklemoon.livejournal.com]

Seconded.

[blk]

Nifty! I feel safer on the rocks already. :)

[whuffle.livejournal.com]

Hey, cool test and visuals! Especially being someone who owns quite a few of this style of slings and climbs on them every year.

[spitcurl.livejournal.com]

I love The Machine That Breaks Things. :)

[lyonesse.livejournal.com]

how workable/sewable are they, and how wide, and how soft? they might make good horse tack.

[klingonlandlady.livejournal.com]

they're maybe a little wider than half an inch, and a little thinner than 1/8" thick? Pretty soft and sewable.

[lyonesse.livejournal.com]

where do you get them?

sounds worth playing with!!

(all my wrists need is another hobby....;)

[frobzwiththingz.livejournal.com]

REI, ems, or other places that carry climbing gear. Sterling makes 1-inch versions of these as well. If you really want to try making horse tack out of them, you might consider calling the manufacturers directly and see if they'll sell you lengths of the raw sling material itself.

[rmd.livejournal.com]

hooray for tMtBT!

[whale-girl.livejournal.com]

Wow. I'm impressed. Spectra is good stuff.

See ya weds -- I should finally be in town on a silks night!

[deguspice.livejournal.com]

Something for you to try next time.
http://www.caves.org/section/vertical/nh/50/knotrope.html

[mikeys.livejournal.com]

Hello good sir! You've got a lot of fun technical aerials related stuff buried in your lj posts, and I was wondering if you would mind me drawing attention to it over on troupedeveloppe?

I've really enjoyed reading about it, and I think others would as well :)

(Specifically, trap & lyra bar construction, mark2 rig, and the silks break load testing.)