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Author Topic: What determines a rope's strength, flexibility and abrasive characteristics?  (Read 7322 times)

Offline ctyre34

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Hello,
My Name is Thomas and I am doing a report on the characteristics of rope in three different areas, Strength, Flexibility, and Abrasion. I have a few questions about certain areas of my project.
Thanks in advance,
1. When rope is put under pressure is its maximum working load the point where it breaks?
2. Which ropes would you recommend for being able to hold a weight? Pulling something? Durability?
3. If a rock climber were to go rock climbing, what rope would you suggest they use? Why?
4. What is your classification on rope? Is there different subgroups that you feel that different ropes go under?
5. When I took rope and attached it to a pole and then pulled it back with a forklift, why did the rope shoot back like a slingshot the other direction it was being pulled?
6. Why do ropes have a maximum working load? Is that there breaking point?
7. If you were going to pull a trailer full of heavy materials what rope would you use? why?
8. In your opinion, do you think rope gradually loses its strength after usage? If so why?
« Last Edit: 12/01/2012 04:02:53 by chris »


 

Offline Geezer

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When rope is put under pressure is its maximum........


Your knowledge of ropes seems a bit, er well, ropey.
 

Offline CliffordK

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I would go to a specialty store if you are planning on doing any rock climbing.  Or...  perhaps hunt down a specific rock climbing website to ask about gear.  You don't want to have a 20 foot fall into a rope...  with 100 feet of cliff below you as a test for tensile strength and abrasion resistance of your rope. 

In many cases, you should not go "cheap" for critical safety gear.

Typically your reported maximum working load will have an error margin that should be listed somewhere, perhaps on the packaging.  Abrasion, or aging could affect it.

In rock climbing, as mentioned, you will need supplies that are able to arrest a fall, so while a piece of ordinary bailing twine can support 100% of your weight applied statically, it might not support your weight if you plunge 20 feet and expect to be caught by the twine.
 

Offline Don_1

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1. When rope is put under pressure is its maximum working load the point where it breaks?

Rope is usually supplied as having an SWL (Safe Working Load); this will be well within its tested 'breaking strain'.

2. Which ropes would you recommend for being able to hold a weight? Pulling something? Durability?
This would depend on the individual circumstance. Natural rope (made from sisal) can stretch to some degree, where polypropylene rope would be less likely to stretch. As far as durability is concerned, sisal is extremely durable and resistant to deterioration by sea water.
 
3. If a rock climber were to go rock climbing, what rope would you suggest they use? Why?

Since natural rope is absorbent, polypropylene might be best in this instance. A climber would not want to be carrying more weight than absolutely necessary, which might well be the case with rope which has become wet due to rain, snow/ice melt or condensation.

4. What is your classification on rope? Is there different subgroups that you feel that different ropes go under?
I'm guessing that the main classifications would be Natural, Man Made and Steel. Breaking these down into subgroups might be based on the actual fibres and gauge of the fibres, elasticity, absorption, friction, weight and breaking strain of the individual fibres.

5. When I took rope and attached it to a pole and then pulled it back with a forklift, why did the rope shoot back like a slingshot the other direction it was being pulled?
Any rope will have a degree of elasticity, even steel. The recoil when it breaks will be just the same as you would expect from an elastic band when it breaks, except rope may have a far more devastating effect. The pole may also have contributed to the recoil.
NB. Using a fork lift truck to break a rope is not what FLT's are designed for and could pose a very significant danger.

6. Why do ropes have a maximum working load? Is that there breaking point?
So the user knows which rope is safe to use for a particular purpose. See Q1 above.

7. If you were going to pull a trailer full of heavy materials what rope would you use? why?
I wouldn't use rope at all because of its elasticity. A solid, rigid coupling would be safer and more controllable.

8. In your opinion, do you think rope gradually loses its strength after usage? If so why?
Yes. The more it is used and exposed to the elements the faster it will deteriorate. That said, sisal rope coils were found by archaeologists working near the Red Sea in Egypt which have been dated as 4000yrs old.
 

Offline Mazurka

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1. When rope is put under pressure is its maximum working load the point where it breaks?

As Don says, maximum (safe) working load should be well below the breaking strain. 

It is worth remembering that in reality the strength of a rope is dictated by its weakest part which is normally a knot.  (This is why in lifting applications strops or chains are used to avoid the need to knot)

2. Which ropes would you recommend for being able to hold a weight? Pulling something? Durability?

It entirely depends on the circumstances – the nature of the load, the nature of the anchor point etc.  Natural fibres tend to swell when wet – which can be an advantage or disadvantage. 
Kernmantle ropes (climbing ropes) have a sheath for abrasion resistance protecting the inner core which provides most of the strength.

3. If a rock climber were to go rock climbing, what rope would you suggest they use? Why?
Modern climbing rope is nearly always Kernmantle construction and come in two types – dynamic and low stretch.  Dynamic rope is designed to stretch to reduce the impact of the fall, Low stretch rope is used for fixed ropes, - such as abseiling or in rescue situations, where it may be necessary to use multiple lines to reduce the load / provide backup.  Low stretch rope is stronger and heavier than a dynamic of the same diameter.   

The core is typically a number of strands of polyamide (nylon) spun into laid rope (i.e. looks like a traditional “twisted” rope) with a polyester sheath.  The weave of the sheath determines several of the ropes properties such as abrasion resistance, flexibility and feel.

4. What is your classification on rope? Is there different subgroups that you feel that different ropes go under?

Rope can be classed by material – natural & manmade., These can be  subdivided by specific material (e.g. hemp, coir, sisal, cotton, silk etc & polypropylene, polyester, polyamide, steel etc.

Rope can also be classed by construction – Laid (aka twisted aka hawser) kernmantle and braided

But rope is mainly classified by its properties/ use – e.g. climbing rope, parachute cord, hawser 



5. When I took rope and attached it to a pole and then pulled it back with a forklift, why did the rope shoot back like a slingshot the other direction it was being pulled?

Guess this depends on where it failed.

6. (Why do ropes have a maximum working load?) Is that there breaking point?

No, working load is not the same as breaking strain, but is broadley irrelevant as generally the weak point is a knot.

7. If you were going to pull a trailer full of heavy materials what rope would you use? why?

I would probably try and use a chain or fixed link - far more reliable.  Any particular trailer will have an attachment point depending on what it was designed to be towed with…

8. In your opinion, do you think rope gradually loses its strength after usage? If so why?

Depends on materials and environment – sunlight / uv being a prime cause of deterioration, although poor storage, chemical contamination, abrasion etc.  A dynamic climbing rope is weakened after a fall and depending on the forces (often worked out as “fall factor”) may or may not be useable again.


 

Offline imatfaal

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I do hope that Ctyre comes back and reads the excellent replies above. 

Rope in my world is SWR (Steel Wire Rope) with a safe working load over 100 mt and in sizes so heavy that a person couldnt even begin to lift it.  Nylon ropes are just as strong, but even heavier when wet due to the thickness; however they can be easily handled in small segments (tails) and can be made into loops and bights for tying off. 
 

Offline Geezer

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I do hope that Ctyre comes back and reads the excellent replies above. 

Rope in my world is SWR (Steel Wire Rope) with a safe working load over 100 mt and in sizes so heavy that a person couldnt even begin to lift it.  Nylon ropes are just as strong, but even heavier when wet due to the thickness; however they can be easily handled in small segments (tails) and can be made into loops and bights for tying off. 

Arrr matey! I likes to do me own eye splices so everything on my yacht is all sheepy shape and Bristol City like.

(It's more "economical" too!)

Arrrr!


As the girl from Govan said to the yachtsman from Gourock,

"Yer affa yat? Whit yat are ye affa?"
 

Offline CliffordK

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Rope in my world is SWR (Steel Wire Rope) with a safe working load over 100 mt and in sizes so heavy that a person couldnt even begin to lift it.  Nylon ropes are just as strong, but even heavier when wet due to the thickness; however they can be easily handled in small segments (tails) and can be made into loops and bights for tying off. 
You aren't a fighter pilot are you?
Where a 1.5" cable with a 215,000 breaking strength is the difference between a dry landing and a plunge into the ocean.

Fatigue is also an issue, especially with steel cables.  The Navy replaces their arresting cables with every 125 landings.
 

Offline Geezer

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Fatigue is also an issue, especially with steel cables.  The Navy replaces their arresting cables with every 125 landings.


They probably ruled out nylon rope because of its elasticity. It might tend to re-launch the aircraft backwards after it had landed.
 

Offline CliffordK

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There was actually a TV special on arresting cables recently.  It is quite a complicated thing.  They don't just pull a cable tight across the deck, but have some complex mechanics to deploy the cable like a spring when the plane lands...  and thus give it a significant amount of space to decelerate.

Cables have been a mainstay for years, but there is always interest in new composite materials. 

Spiders, apparently, have engineered their webs to have both tension segments and stretch segments, which would help a lot with fatigue.  And, they have a tremendous ability to bounce, or resist the wind.
 

Offline Geezer

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They don't just pull a cable tight across the deck, but have some complex mechanics to deploy the cable like a spring when the plane lands...  and thus give it a significant amount of space to decelerate.


You are quite correct. The cable is only a means to transfer the aircraft's kinetic energy to a brake.
 

Offline RD

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Any rope will have a degree of elasticity, even steel. The recoil when it breaks will be just the same as you would expect from an elastic band when it breaks, except rope may have a far more devastating effect.

https://en.wikipedia.org/wiki/Tug_of_war#Arm_severing_incident
« Last Edit: 13/01/2012 16:07:04 by RD »
 

Offline ctyre34

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You guys are truly amazing! Your responses were just what I wanted. Thank you for your generous understanding and tolerance to deal with such simple questions. Sorry for my lack of knowledge. THANK YOU SO MUCH! You are all wonderful  ;D
Thanks,
Ctyre
 

Offline imatfaal

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Never apologise for a lack of knowledge - everyone is missing knowledge in most areas; the only thing to apologize for would be if you were not to ask for aid or not to appreciate any help - and you avoided those traps with ease. 

Feel free to stick around - maybe next time you will be the one answering the questions.  :-)

 

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