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summerprophet
May 18, 2009, 9:16 PM
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Recently I was involved in a discussion in another thread regarding rope strengths.
I know that I have been taught for rigging that assume the rope has a strength of 30kN and build all systems to be as strong or stronger.
Those opposed to my statements brought up test data of static loading being able to break ropes in the 8 kN range.
It was my understanding that this give erronius data as this is not the situations in which dynamic ropes are used.
My question is this? Why is the data erronius?
I am guessing here, but perhaps someone with more of a physics background can set me right.
Is it this? Static pull testing is bases upon minimum deformation of the sample (before failure), to obtain accurate results. And the very nature of climbing ropes is to deform under load, thus from the very beginning of the test, the data is incorrect.
I know the UIAA does not use static testing at all for climbing ropes, everything is dynamic loads.
Anyone care to educate me on this further?
(This post was edited by summerprophet on May 18, 2009, 9:18 PM)
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roy_hinkley_jr
May 18, 2009, 9:27 PM
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Where is the data showing dynamic ropes break at 8 kN in a static pull? Most tensile testers capable of generating enough force don't have sufficient throw to accommodate all the stretch.
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geezergecko
May 18, 2009, 9:37 PM
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Isn't 8kN what most ropes endure on the first drop of the UIAA test, and on the second and subsequent drops this force goes up as the rope loses it's dynamic properties and essentially becomes a wire? 8 kN static breaking load sounds erroneous to me.
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kennoyce
May 18, 2009, 9:45 PM
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The reason that in static loading the rope breaks at such a low force is because of the rope stretch. Basically once you reach the ropes maximum impact force rating load, the force will not go up, but the rope will continue to stretch further and further until it breaks. In this case it isn't the force on the rope that is breaking it, it is actually the distance the rope has stretched.
Hope this helps.
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JimTitt
May 19, 2009, 7:21 AM
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Static ropes which riggers use are much stronger than dynamic climbing ropes, rule of thumb would be double.
Most (quasi) static bollard tests give strengths for NEW climbing ropes in the range of 17 to 22kN.
That USED ropes lose ca. 50% of their strength is well known and researched.
Climbing ropes are the dynamic element in the safety chain, their funtion is purely to convert energy into force and they only need to be strong enough to do this. Since the force is limited by the CE/UIAA standard to 12kN for the FIRST drop for a new rope then a rope with a breaking strain of 12kN is obviously good enough except an allowance has to be made for the weakening of the knot.
Quasi-static testing is nothing to do with minimum deformation, the object is simply pulled until it fails, the highest reading obtained during the pull being the breaking strength of the object. This is brutally simple and accurate.
For some pull tests with various ropes and knots on new ropes and also to satisfy the poster who has obviously never seen a standard test rig go to http://www.caves.org/.../nh/50/knotrope.html
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majid_sabet
May 19, 2009, 7:30 AM
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Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half.
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USnavy
May 19, 2009, 4:02 PM
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majid_sabet wrote: Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half.
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fitzontherocks
May 19, 2009, 4:13 PM
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Are their values in pounds? (It seems so, but I didn't want to assume.)
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majid_sabet
May 19, 2009, 5:24 PM
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USnavy wrote: majid_sabet wrote: Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half. Once again your pulling numbers out of your ass and commenting on something you know nothing about (what’s new). The maximum elongation a rope can withstand before it breaks is extremely dependent on the rope and many other factors. Saying ropes break once they stretch to 150% of their fundamental length is like saying all cars will sustain transmission damage if you drive faster then 140 MPH...
I am going to save this cause this one comment from you will take you down in RC lab once for all.
just watch
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pfwein
May 19, 2009, 5:40 PM
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summerprophet wrote: It was my understanding that this give erronius data as this is not the situations in which dynamic ropes are used. My question is this? Why is the data erronius?
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adatesman
May 19, 2009, 6:01 PM
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JimTitt
May 19, 2009, 6:11 PM
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Well I assumed they are since all the notes are in lbs and everything else is in Imperial unuts. And the guys are from Texas where a kilogram is probably only a unit of weight in the drug smuggling industry!
Jim
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Rudmin
May 19, 2009, 7:04 PM
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USnavy wrote: majid_sabet wrote: Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half. Once again your pulling numbers out of your ass and commenting on something you know nothing about (what’s new). The maximum elongation a rope can withstand before it breaks is extremely dependent on the rope and many other factors. Saying ropes break once they stretch to 150% of their fundamental length is like saying all cars will sustain transmission damage if you drive faster then 140 MPH...
Majid clearly stated that he was talking about ropes stretching to 50% of its original length not 50% more than its unweighted length. What he is referring to of course is the breaking strength when you cut a rope in half to mark the middle. He is always being cryptic like that and you fell for his games once again.
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bigo
May 19, 2009, 7:11 PM
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JimTitt wrote: Static ropes which riggers use are much stronger than dynamic climbing ropes, rule of thumb would be double. Most (quasi) static bollard tests give strengths for NEW climbing ropes in the range of 17 to 22kN. That USED ropes lose ca. 50% of their strength is well known and researched. Climbing ropes are the dynamic element in the safety chain, their funtion is purely to convert energy into force and they only need to be strong enough to do this. Since the force is limited by the CE/UIAA standard to 12kN for the FIRST drop for a new rope then a rope with a breaking strain of 12kN is obviously good enough except an allowance has to be made for the weakening of the knot. Quasi-static testing is nothing to do with minimum deformation, the object is simply pulled until it fails, the highest reading obtained during the pull being the breaking strength of the object. This is brutally simple and accurate. For some pull tests with various ropes and knots on new ropes and also to satisfy the poster who has obviously never seen a standard test rig go to http://www.caves.org/.../nh/50/knotrope.html
Thanks Jim, that is a good post with good rationale.
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USnavy
May 20, 2009, 4:00 AM
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Rudmin wrote: USnavy wrote: majid_sabet wrote: Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half. Once again your pulling numbers out of your ass and commenting on something you know nothing about (what’s new). The maximum elongation a rope can withstand before it breaks is extremely dependent on the rope and many other factors. Saying ropes break once they stretch to 150% of their fundamental length is like saying all cars will sustain transmission damage if you drive faster then 140 MPH... Majid clearly stated that he was talking about ropes stretching to 50% of its original length not 50% more than its unweighted length. What he is referring to of course is the breaking strength when you cut a rope in half to mark the middle. He is always being cryptic like that and you fell for his games once again.
The only thing that is clear to me is that he does not understand the relation of percentiles and the definition of the word stretch. Stretch implies an increase in length. Referring to the value of 50% implies a decrease of 1/2 from the fundamental value or half of the fundamental value.
So accordingly it’s impossible for anything to stretch to 50% of its length because stretch implies an increase and 50% implies a decrease, or part thereof.
It’s possible for an object to stretch to 150% of its fundamental length.
It’s possible for an object to stretch 50% beyond its fundamental length.
It’s possible for an object to shrink to 50% of its fundamental length.
Now one may argue that it’s possible for an object to stretch to -50% of its original value but that’s not what he implied
But it’s not possible for an object to stretch to 50% of its fundamental length. If the object is 50% longer then its fundamental value it stretched 150% of its fundamental value, or 50% beyond its fundamental value. If the object is 1/2 the length of its fundamental value, it shrunk to 50% of its fundamental value.
(This post was edited by USnavy on May 20, 2009, 4:09 AM)
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majid_sabet
May 20, 2009, 6:39 AM
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adatesman wrote: Good point Majid. We're in The Lab guys, so keep things civil and on topic. Therefore no picking on Majid, and Majid- no trolling in The Lab. Not to say I think you're trolling here... I have no doubt whatsoever that those pics are genuine and will take you at your word about what you say you were told. I've got bigger things to deal with at the moment to keep an eye on this, but rest assured if I come back and people aren't playing nice I won't be happy.
I am not trolling and what i said is within the Lab guideline but our navy commando blow a 10 amp fuse on a 500 watt light bulb. What I said was not made up and there are science behind it but I just can't find my document on it. I am sure Sterling jim could reset his fuse by confirming that my statement which I am certain is not that far from that 50%.
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majid_sabet
May 20, 2009, 6:47 AM
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USnavy wrote: Rudmin wrote: USnavy wrote: majid_sabet wrote: Dill told told me once, when a dynamic rope stretches to 50% of their original length, they will snap in half. Once again your pulling numbers out of your ass and commenting on something you know nothing about (what’s new). The maximum elongation a rope can withstand before it breaks is extremely dependent on the rope and many other factors. Saying ropes break once they stretch to 150% of their fundamental length is like saying all cars will sustain transmission damage if you drive faster then 140 MPH... Majid clearly stated that he was talking about ropes stretching to 50% of its original length not 50% more than its unweighted length. What he is referring to of course is the breaking strength when you cut a rope in half to mark the middle. He is always being cryptic like that and you fell for his games once again. The only thing that is clear to me is that he does not understand the relation of percentiles and the definition of the word stretch. Stretch implies an increase in length. Referring to the value of 50% implies a decrease of 1/2 from the fundamental value or half of the fundamental value. So accordingly it’s impossible for anything to stretch to 50% of its length because stretch implies an increase and 50% implies a decrease, or part thereof. It’s possible for an object to stretch to 150% of its fundamental length. It’s possible for an object to stretch 50% beyond its fundamental length. It’s possible for an object to shrink to 50% of its fundamental length. Now one may argue that it’s possible for an object to stretch to -50% of its original value but that’s not what he implied But it’s not possible for an object to stretch to 50% of its fundamental length. If the object is 50% longer then its fundamental value it stretched 150% of its fundamental value, or 50% beyond its fundamental value. If the object is 1/2 the length of its fundamental value, it shrunk to 50% of its fundamental value.
Here is another explanation so I hope you understand without blowing the power supply
Example; a dynamic rope is 60 meter in length ( no load)
when you pull this dynamic rope to 50% of its original length(additional 30 meter of stretch)
So now this rope is @ 90 meter in length (60 + 50% of 60 =30 meter from end to end), it has high probability to snap in half.
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knudenoggin
May 21, 2009, 6:48 PM
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summerprophet wrote: I know that I have been taught for rigging that assume the rope has a strength of 30kN and build all systems to be as strong or stronger.
some better indication of it--half-inch SAR ropes might be so beefy,
but there are varieties of ropes & strengths even there.
2) Why should the system be stronger than the rope? If the rope's
a critical element (as it is in climbing--as opposed to each placement
of support up a route), one might want to ensure that something ELSE
breaks first, in some sort of load-amelioration effect. Of course,
mostly one is aiming to be big margins stronger than possible loads,
and in this sense building to be stronger than rope is just keeping up
the average.
In reply to: Those opposed to my statements brought up test data of static loading being able to break ropes in the 8 kN range.
issue of loading. I know someone who is well versed in physics and
has a heartbreak each time someone advances the belief that there
is great effect from "shock-loading"; he has studied load plots and
found speed of loading to be insignificant in some number of cases.
Rapid loading of a knot has been theorized to lead to greater weakening
by frictional heat generation (Dave Merchant, Life on a Line),
and the effect of arresting the movement of a mass varies depending
on speed. But the forces at which the material fails is largely
independent of load rate, it seems.
-----
As far as I got in the gratuitously acrimonious *debate* between
Major Sorbert & USN, yes, the extension at rupture will be a different
value per different rope--sometimes as much as 50% stretch in climbing
ropes! In this regard, it's rather interesting to see the cited elongations
at rupture for nylon fibres--MUCH less!? Take a look at some of the
rope data information pages at Yale, Samson, New England, ... sites.
*kN*
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JimTitt
May 22, 2009, 6:26 PM
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Not wishing to enter the "debate" as you nicely put it but some of us can remember times before the UIAA/CE Norms when the British Standard for climbing ropes in the U.K. gave merely a breaking load (2tons) and required a MINIMUM extension of 50% before breaking.
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kennoyce
May 22, 2009, 6:39 PM
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This is probably where majid got his 50% value from. If the norm used to be that a rope must be able to stretch 50% from its original length I would assume that most ropes still fall close to this value.
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