the Machine that Breaks Things claims some more victims
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.
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.