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Chockstone Forum - Gear Lust / Lost & Found

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Author
Slackline - fatigue effects on biners?
alg
15/06/2010
5:35:55 PM
one for the engineers/metallurgists...

I'm putting together a slackline using some old biners etc, and was just thinking whether they'll be ok to use climbing again.

The loads in a slackline should be under 3kN, peak loads reaching 6ish (max), but there's a fair bit of cyclic loading due to jumping/bouncing etc. is there any chance of fatigue failure? The biners are aluminium, and heavy scratching could be a factor...
From what I can work out it should take 10,000,000 plus cycles but just thought i'd see if anyone had any thoughts.
mikllaw
15/06/2010
5:50:19 PM
I think the loads might be much higher, if I wasn't jet lagged I'd work it out, but I saw some bolts that a slackline had been clipped to, looked more like 10 kN at a guess.

If the angle in the slackline is 170 degrees, the multiplication is about 12. There isn't much dynamic laoding (the stretch in the system takes care of that) so lets assume your bodyweight plus a bit of dynamic load = 1 kN, that's 12 kN straight off.


I'd guess that the pins in the gate would fail first. Wide tape in a skinny biner would increase the force on these a lot.


IdratherbeclimbingM9
15/06/2010
5:54:36 PM
On 15/06/2010 alg wrote:
>I'm putting together a slackline using some old biners etc, and was just
>thinking whether they'll be ok to use climbing again.
>
True old karabiners are steel! They would easily handle the task. Get a dedicated set for your slackline, as they are too heavy for general climbing purposes.
vonClimb
15/06/2010
6:37:52 PM
I was speaking to some guys in the states about the chances of them breaking. They spoke of a case where a biner snapped and then hit the guy slacklining and broke his leg.

Kinda of a scary thought. Needless to say I use steel biners now
alg
15/06/2010
8:50:41 PM
On 15/06/2010 mikllaw wrote:
>I think the loads might be much higher, if I wasn't jet lagged I'd work
>it out, but I saw some bolts that a slackline had been clipped to, looked
>more like 10 kN at a guess.
>
>If the angle in the slackline is 170 degrees, the multiplication is about
>12. There isn't much dynamic laoding (the stretch in the system takes care
>of that) so lets assume your bodyweight plus a bit of dynamic load = 1
>kN, that's 12 kN straight off.


Yeah, i calculated 2.8kN for a 100kg person with a 10degree sag in the line. The dynamic load all depends on how far you assume it to give, if a 100kg person jumps and lands with stiff legs (which they probably won't) and the line only gives 30cm the load could be up around 15kN.
considering the bolts you saw i might just buy some steel biners though...

cheers
Paul
15/06/2010
9:13:16 PM
Or even better, use some massive steel mallions, like the 12mm ones. stronger than any carabiner and you can get square or triangle ones which would be a better suited shape for slack line purposes.
One Day Hero
16/06/2010
3:20:31 PM
On 15/06/2010 alg wrote:
>one for the engineers/metallurgists...
>
>From what I can work out it should take 10,000,000 plus cycles but just
>thought i'd see if anyone had any thoughts.

Its not actually engineers whom you seek, do you think someone can just jot out an accurate answer to that question on a piece of paper?

Rather than theorists, ask the guys in the lab........there are thousands of people out there logging thousands of hours boinging on exactly the same setup you will use. I don't know why they do it, seems rather boring to me.....but, the experiment has been done and will yield much more useful info than wanky speculation.

So, anybody broken a biner slacklining? Seen one break? Have reliable reports of them breaking?

My guess is that it doesn't happen cause you'd have heard about it already...........hey, why can't you afford 4 old biners for slackline duties? Are you a single mum?

Climboholic
16/06/2010
3:48:13 PM
I broke a biner on the weekend.
I was out trail biking when I saw a P plater go down a road that I knew he'd never get through in his work ute. Anyway, half an hour later he came walking up to out camp asking for a tow. I asked him if he had a snatch strap and he said yes but nothing to hook it up with. I had a 25kN biner in the car so I did a quick calculation and figured 2.5 tonnes should do it. I manoeuvred the Forester into position, hooked it up and gave it a go. The biner snapped on the second try. I scratched my head and wondered why it had failed. Then I asked him again if it was a STRETCHABLE snatch strap? "Ahh, no, maybe not". Evidently the dynamic load from the momentum of the car exceeded 25kN.
Some people should be banned from going outdoors.
random
16/06/2010
4:00:05 PM
Fatigue and failure. Definetly. I have broken a carabiner which shot back towards me at warp speed and the line (Multiple times) before. I have even heard of the line hitting people so hard it has flipped them over. Let alone a metal carabiner. Death? If your slacklining dont use yuor climbing gear. Either dedicate some gear to slacklining or purchase a commercial slackline (Gibbon Slacklines or the like).
alg
16/06/2010
4:08:23 PM
On 16/06/2010 One Day Hero wrote:
>On 15/06/2010 alg wrote:
>>one for the engineers/metallurgists...
>>
>>From what I can work out it should take 10,000,000 plus cycles but just
>>thought i'd see if anyone had any thoughts.
>
>Its not actually engineers whom you seek, do you think someone can just
>jot out an accurate answer to that question on a piece of paper?
>
>Rather than theorists, ask the guys in the lab........there are thousands
>of people out there logging thousands of hours boinging on exactly the
>same setup you will use. I don't know why they do it, seems rather boring
>to me.....but, the experiment has been done and will yield much more useful
>info than wanky speculation.
>
>So, anybody broken a biner slacklining? Seen one break? Have reliable
>reports of them breaking?
>
>My guess is that it doesn't happen cause you'd have heard about it already...........hey,
>why can't you afford 4 old biners for slackline duties? Are you a single
>mum?

I was only after a ball-park figure/experienced opinion, fatigue failure's fairly predictable.

There're heaps of conflicting opinions and stories out there, people who've used alluminium wiregates for years without a problem and people who've snapped lockers and broken their legs. I thought maybe a bit of wanky speculation'd be handy in weeding out the bullshit. Plus i was interested.

...gotta go, my kids are fighting
One Day Hero
16/06/2010
4:14:50 PM
On 16/06/2010 random wrote:
>Definetly. I have broken a carabiner which shot back
>towards me at warp speed

Well, there you go. I'm quite surprised that someone on this forum has personally busted a biner slacklining but they have........so, not much point doing maths bullcrap. Biners don't fail often in slacklines but it does happen, the mallions might be a good idea after all.
ET
16/06/2010
4:18:44 PM
On 16/06/2010 One Day Hero wrote:
>Its not actually engineers whom you seek, do you think someone can just
>jot out an accurate answer to that question on a piece of paper?
>
>Rather than theorists, ask the guys in the lab........there are thousands
>of people out there logging thousands of hours boinging on exactly the
>same setup you will use. I don't know why they do it, seems rather boring
>to me.....but, the experiment has been done and will yield much more useful
>info than wanky speculation.
>
>So, anybody broken a biner slacklining? Seen one break? Have reliable
>reports of them breaking?
>
>My guess is that it doesn't happen cause you'd have heard about it already...........hey,
>why can't you afford 4 old biners for slackline duties? Are you a single
>mum?

Here's a wanky's theoretician's 2 cents worth...
http://www.physics.usyd.edu.au/~et/slackline.pdf
Feel free to criticise/make corrections...

Though I would like to add engineers are the people with equipment to measure the breaking force of your biners... It's not all done on paper...

However given the time and information I assure you that a wanky theoretician can make a fairly accurate model of the system and provide much more insight of what's happening in your setup... and can tell you if your record breaking highlining attempt is going to likely end in your death or not...

Anyway, you may notice the lack of values in the pdf as couldn't easily find spring constants for nylon webbing, but I plugged in values which I thought were "reasonable" and tension on either biners never exceeded 10 KN...

If someone has more time than me (looking at the Klaw...) feel free to show otherwise, by either showing me what I did wrong, setting up an experiment to measure the force on the slackline (I imagine the equipment/setup would be similar to your break test ones) or any other means...

ajfclark
16/06/2010
4:34:29 PM
On 16/06/2010 random wrote:
>Definetly. I have broken a carabiner which shot back towards me at warp speed

What happened just prior to the carabiner snapping? What it a locking or non-locking biner? Do you have the pieces?

I've noticed that there can be a lot of vibration in a slackline system (particularly during a messy dismount). If non-locking biners are used, could this flutter the gate on them? I would've expected the the force of the line to keep the biners closed, but if the gate did flutter I wouldn't be surprised if a biner snapped even if the line is only applying 10kN.
One Day Hero
16/06/2010
7:44:12 PM
On 16/06/2010 ET wrote:
>Though I would like to add engineers are the people with equipment to
>measure the breaking force of your biners... It's not all done on paper...
>
>
>However given the time and information I assure you that a wanky theoretician
>can make a fairly accurate model of the system and provide much more insight
>of what's happening in your setup... and can tell you if your record breaking
>highlining attempt is going to likely end in your death or not...
>
Gaah! You don't need a "fairly accurate model of the system". The actual system is very simple and actual experiments in the real world conditions (which you were hoping to model) are being performed everyday by climber bums in campgrounds around the world. I find it astonishing that supposedly educated people seek to answer a question about what happens to biners in slacklines by getting out a computer simulation!?! And that someone would kick off a hacker analysis of whether they can climb on slackline biners?????

I'll tell you how it will play out; There will be much simulating and theorising. Maybe, if we're lucky, a blue thing will appear. A concensus shan't be reached, yet most analysts will concur that the biners are almost certainly ok,.......but, for $20 don't risk it.

Done! Any more posts will only circle back to this spot in the end

Hugh
16/06/2010
8:26:20 PM
seems like some people on here don't enjoy using that thing we call a brain.... Nothing wrong with theorising... In fact, it's actually hypothesising.. A theory has been tested ;-)

Note: physics nerds, don't argue thought experiment as theory
alg
16/06/2010
9:05:31 PM
ODH, it's not the destination but the journey mate. I could tell the outcome of you throwing your opinion on the majority of the threads in this forum and save you the time, but it wouldn't be the same, would it?

ajfclark
17/06/2010
2:41:41 PM
From http://www.nwslackline.org/453/primitive-tension-testing-results :
Last I added my double-pulley multiplier and pulled the line to a crispy 826lbs, which loosened to 740lbs over the next few minutes. I hopped on the line and bounced hard, seeing peak numbers around 1100lbs. Getting off the line, it then had stretched to 630lbs of tension. This number slowly rose and then capped around 650lbs. Again I bounced, seeing peak numbers around 1050lbs. After getting off this time the line read 610. It slowly tightened up to 620lbs
225lbs to the kN right? So the peak he saw was 1100/225 = 4.9kN?

This looks interesting too:

http://www.nwslackline.org/478/destructive-testing

ajfclark
17/06/2010
3:19:04 PM
Here's another video of them rigging a line by hand with a force cell inline: http://www.youtube.com/watch?v=CZBC4IW55XM Max seen here is 1076/225 ~= 4.8kN
One Day Hero
20/06/2010
2:08:05 PM
On 16/06/2010 alg wrote:
>ODH, it's not the destination but the journey mate. I could tell the outcome
>of you throwing your opinion on the majority of the threads in this forum
>and save you the time, but it wouldn't be the same, would it?

It's not much of a journey though, is it? Given that you need your climbing gear to have a very low chance of failure and someone has already piped up and said that they've busted a biner with a slackline........where do you go from there? Get a hypothesis up and running, do some modelling and tell everyone that its fine to use slackline biners? Bit hard to argue that point when someone has actual evidence that you're wrong.

Now, if you want an interesting journey..........

I'm thinking of getting myself guided up everest; gear hauled for me, lines fixed for me, desicions made for me, logistics taken care of for me, the full deal...........then, I'm going to write a book about my adventure and kick off a career, charging $1000 bucks an hour as a motivational speaker (with my massive triumph over everest as the central subject matter).

Is everyone happy to support my dream.......or do you feel that my climbing is merely a career move, and that I'm planning nothing more adventurous than the prostitution of an already slutty mountain for my own financial benefit?

There are 19 messages in this topic.

 

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