Ever wonder how many load cycles your carabiner can take?

[PseudoFission]

http://web.mit.edu/sp255/www/reference_ ... tation.pdf

It depends on the average load - but for the loads experienced in most vertical caving - you're looking at tens of thousands of cycles. For most people this probably translates to hundreds of years worth of use. In short - you will likely retire your carabiners for other reasons long before cyclic loading (fatigue stress) is ever an issue (from vertical caving).

[chh]

Thanks for posting that. It's cool to see folks thinking about testing in different ways. The one thing that leapt out at me, "decreasing carabiner weight will likely result in a decreased life forcing the need for fatigue ratings"
I wonder if that will ever happen? I wonder if the results would be much different on some of todays ultralight biners?

[NZcaver]

Honestly, no I've never wondered how many load cycles my carabiner can take.

I'm not a climber, so if I take (severe) falls or subject carabiners to significant shock loads of 20kN I'm obviously doing something very wrong.

A couple quick thoughts about this "Analysis of Fatigue Failure in D-shaped Carabiners."

Kudos to the MIT people for trying a new approach for making carabiners fail by introducing repeated cyclic loading at high forces. But I'm not convinced their 20kN ballpark figure has much real-world relevance. Thats a pretty big shock load, even given the psuedo 2-to-1-ish MA effect on the first piece of protection and carabiner (see page 4). The diagram shows a falling climber generating 12kN, and a resulting 8kN being transferred to the belayer. Please! I know the nominal UIAA maximum impact standard for ropes is 12kN, but really who takes severe falls like that on a regular basis? And even if some do, the peak force experienced by that first carabiner will surely be lessened by the stretch in the dynamic rope, and the flexible belayer reacting at the other end.

I'd like to know if the participants actually went to a cliff or indoor wall with a peak force dynamometer and took some real-world measurements with live climbers. The other reason why 20kN sounds bunk to me is that most of my (alloy) D-shaped carabiners have MBS ratings varying from about 20kN to 35kN. MBS = Minimum Breaking Strength, NOT maximum safe working load. I realize the construction, ratings, and mechanisms of failure are different for carabiners than for Maillon Rapide screw links, but humor me for a moment. If we were to apply the standard 5:1 MBS/SWL ratio used for Maillon Rapides, we could roughly assume that the maximum load we should safely be applying to a 20kN carabiner would be 4kN. (20/5=4) Or 7kN on a 35kN rated carabiner. Alloy carabiner failure caused by repeated cyclic loading up to 20kN is interesting to observe, but if that is indeed a real-world concern then perhaps climbers need to start using big steel carabiners.

Anybody have other thoughts about this?

[PseudoFission]

Oh yeah - the projected forces in the beginning of the presentation are way off. My guess is that they found some static test info on FF2s (which used steel plates and a tied off short lanyard) and based the estimate off of that. There is no way a properly belayed lead climber using a dynamic rope could generate those forces, short of doing something far outside the scope of proper technique. In fact I would wager that even in the hardest falls using the least dynamic belay devices (grigri/cinch) the top piece would be hard pressed to see 10kn, roughly half of that on the climber and belay.

Craig Connally's description in "The Mountaineering Handbook" lists tube devices as slipping at 2-2.5kn which limits the belay side forces to that and puts a ~2kn force on the climber. My friend Dan took a huge lead fall 30+ ft total on a sheer vertical wall once. His brother was belaying him with a tube device (atc) I think and gave him a good dynamic catch by running closer into the wall. Dan's last piece was a piton he clipped a shorty yates screamer on - and it didn't even blow during the fall (they're rated to blow at 2kn or 450lbs, and this was on the top piece seeing 1.5x the force the climber experienced). So I believe Craig Connally, who estimates most lead falls are only ~2kn on the climber. Plus - OSHA has a safe max shock load of 8kn - but for a full body work harness. I can tell you personally that anything more than around 1000lbs (~5kn) will REALLY hurt in a climbing harness, and if climbers had to take 5+kn forces in falls - they would NOT be taking lead falls (at all).

NZ you had the same reaction I did - who in their right mind would use a piece of equipment with a possible working load so close to the MBS? Certainly not a very high safety factor. But also keep in mind the cyclic loading tests they do is a random variation of loads with the highest being the number they list. So for a 20kn test they randomly loaded the carabiner from .5kn-20kn. Despite the fact, it's good data for getting an idea of what they can take. Especially when you start to extrapolate your own data based on your very low (comparatively) loads you use for your hobbies.

[PseudoFission]

chh - I also paused reading the part about newer ultralight designs, and sheepishly thought of the last batch of super light carabiners I bought. It seems especially relevant as more manufacturers seem to be reducing weight with clever structural modifications to the design of the carabiner itself. That seems like a whole new dynamic in the world of fatigue testing (maybe not though).

NZ you 'never' wondered how long a carabiner would last?? Not even once? Fair enough. I think the reason is because there isn't a trail of dead bodies to cause any concern. To me it offers more answers in the complex question of system safety factors, and it's reassuring to have some idea of the limits. That and I'm just a geek...

I've already convinced one of my friends to take some lead falls when the weather warms up. We'll get some good data plots for different belay devices and post a few.

[NZcaver]

NZ you 'never' wondered how long a carabiner would last?? Not even once?

You misread my comment. What I said was I've never wondered about how many load cycles my carabiner can take. At least not that I can recall. I do wonder about a lot of things, and I certainly have wondered how long carabiners would last. Some collegues who also wonder about such things have destruction tested carabiners by pull-testing after beating on some of them with hammers. No significant difference. I've actually retired a couple of worn (groovy) carabiners over the years, but never because of cyclic loading concerns. I'm pretty confident my carabiners have never experienced more than 2-3kN at most.

You've confirmed what I suspected about their worst-case methodology. The loads are a little extreme for a climbing study, in my opinion.

[chh]

I agree that the assumptions they made about peak forces were high. A 12kn force on the climber's side would flirt with harness failure, and would definitely injure the person. 20kn on the first piece is, as you guys have already said, too high for a real world scenario when there is ANY rope out at all. I think it's probably even high for a ff2 on a belay anchor in a climbing scenario. Rope slippage still counts there. Static lanyards are a different story, but it still seems unlikely.
The manner of the testing is what interested me. Data can be represented in all kinds of ways, but the implement they were using shouldn't have much inherent error. Most destructive tests are based on failure with a limited number of force applications. This test just confirmed that carabiners can take a lot and keep on ticking. Which we knew already. I think it's great that people continue to TRY and mimic real world scenarios in their testing because that is, after all, where we use the stuff. This wasn't the be all and end all in cyclical loading studies, but it was an interesting experiment nonetheless.
nzcaver, I have also retired groovey carabiners, mostly because of the obvious reduction in mass precisely at the bends, where we know the maximum stress to be. In my mind I know that the overall strength loss would have been minimal, but they just LOOK scary. I'm going to continue placing those ultralight wiregates at the top pieces during a climb and not worry about cyclical loading, but mostly because they don't get loaded that often. Like you said, they're likely good for the rest of my climbing career and beyond.
pseudofission, I'll be anxiously awaiting those dynamometer tests.......