Dyneema Sling Breaking

Over on supertaco there is an interesting thread about joining web slings:
Dyneema Sling Post

One of the recommendations is using this knot instead

That's a little scary. I never use static ropes and I try to avoid girth hitching slings together when I can avoid it. I do have a couple of those super skinny Mammut slings though, so I'll definitley avoid girthing them to something bigger.

Glad to hear the Verm is ok though-- just goes to show you that redundency is always important in your anchors!

Does anybody have any information on girth hitching slings to your harness, either through the belay loop, or through both the legs and waist? Whether you're using shoestrings or normal slings, they're still a lot smaller than what you girth them to on your harness. So what's the deal?

Once again Kolin and crew have come through with some great data that should give all of us pause... check it out.

bdel.com/scene/beta/qc_kp.php

My take is that when new, even when the slings lose 50 percent of their strength, they are still plenty strong for most climbing situations.

But, if you first take into consideration aging of slings, etc. which reduces the overall strength of the sling, then lose 50 percent of that amount, possibly you could run into a dangerous situation.

Thanks, John.

Pause? If anything these results show that Dyneema slings are super bomber, and your rope and or gear is more likely to fail...At least that is what I got out of it.

I got intrigued by the photo of the broken sling. Since I had a similar dyneema sling of the same age which I wanted to retire due to a slight friction burn, I decided to put it through the static load test machine at work. The sling broke slightly below its 22 KN rating at 20.8 KN probably due to the friction burn. It broke at the location of the burn.

Notice that the break is very frayed, not at all clean like the other one that failed under use. I heard what sounded like individual fibers breaking or re-orienting themselves from 2,000 lb to the failure at 4,667 lb. Then SNAP, it went very quickly.

The example which broke under body weight in actual use looks like sabotage to me. The break is way too clean and the load way too low. Even chemicals would probably attack the fibers more randomly than this. I expect that when you leave your rappel setup in place for weeks at a time you never know if a rat is chewing on it or somebody you upset because you took a crow bar to the cliff wants to teach you a lesson.

Shock loading has been mentioned as a culprit. In a very stiff system it can cause high loads from a relatively low weight. Rappelling does not create this, more like a fall factor 2 on a sling girth hitched to your harness and clipped to a bolt. The only way to know would be to simulate this with a force indicator in line with the system. I doubt you could generate 5,000 lb on such a short sling even with a heavy guy. Note that this sling stretched 2.5 inches before it broke.

The girth hitch as a saw theory has some merit. It seems unlikely to me, but who knows. I only have so may slings to break for entertainment so I will have to forgo this test. Do not do this if you are worried, it will probably cause premature wear if it does not break your sling.

To my credibility I actually am an engineer working with mostly composite materials.

Thanks also.

(More of a general audience question)
I guess the most practical of questions, would 2 each 24" dyneema slings of the same width, girthed together, hold a fall starting 10' above protection placement of someone that weighs 185lbs?

Assume a non-dynamic belay using a gri-gri on a belayer's harness fixed to the anchor with no slack in the tie-in system using a PAS as the primary belayer harness tie-in to the anchor. Rope out is 50'. Fall is on vertical terrain -- or better yet, I pitched off an overhang, irregardless, a clean fall.

(if someone could double check that fall factor on the slings. If I'm 10' above my pro using a 4' sling extension, my fall is 24' + dynamic stretch?? -- is that a 2 on the slings no matter what the distance as long as I don't hit anything during the fall?)