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Author Topic: How does stretching wire make it stronger?  (Read 7535 times)

Offline DoctorBeaver

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How does stretching wire make it stronger?
« on: 08/11/2008 00:39:10 »
Watching a program about a crane being restored. They're talking about the steel rope they're going to be using. They showed the rope being made and said that the wire it's made from is stretched to make it stronger and more flexible? I would have thought that stretching it would make it thinner and hence weaken it.

 ???


 

Offline iko

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« Last Edit: 08/11/2008 10:02:51 by iko »
 

Offline RD

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How does stretching wire make it stronger?
« Reply #2 on: 08/11/2008 13:19:45 »
I think stretching to make stronger is "work hardening"...

Quote
in a tensile test a bar of steel is strained to just before the distance at which it usually fractures. The load is released smoothly and the material relieves some of its strain by decreasing in length. The decrease in length is called the elastic recovery, and the end result is a work-hardened steel bar. The fraction of length recovered (length recovered/original length) is equal to the yield-stress divided by the modulus of elasticity. (Here we discuss true stress in order to account for the drastic decrease in diameter in this tensile test.) The length recovered after removing a load from a material just before it breaks is equal to the length recovered after removing a load just before it enters plastic deformation.

The work-hardened steel bar has a large enough number of dislocations that the strain field interaction prevents all plastic deformation. Subsequent deformation requires a stress that varies linearly with the strain observed, the slope of the graph of stress vs. strain is the modulus of elasticity, as usual.

The work-hardened steel bar fractures when the applied stress exceeds the usual fracture stress and the strain exceeds usual fracture strain. This may be considered to be the elastic limit and the yield stress is now equal to the fracture toughness, which is of course, much higher than a non-work-hardened-steel yield stress.

The amount of plastic deformation possible is zero, which is obviously less than the amount of plastic deformation possible for a non-work-hardened material. Thus, the ductility of the cold-worked bar is drastically reduced.

http://en.wikipedia.org/wiki/Work_hardening
 

Offline DoctorBeaver

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How does stretching wire make it stronger?
« Reply #3 on: 08/11/2008 14:14:20 »
Thank you iko & RD
 

Offline ukmicky

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How does stretching wire make it stronger?
« Reply #4 on: 08/11/2008 14:30:11 »
Could it cause the different sized atoms making up the steel wire to line up in a more uniform structure allowing the load to be applied more uniformly to each atomic bond preventing movement and friction of the individual atoms .

Disclaimer

I'm bored have no real idea and I'm only hazarding a way out guess.. ;D

can i still get a thankyou
« Last Edit: 08/11/2008 14:48:08 by ukmicky »
 

Offline DoctorBeaver

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How does stretching wire make it stronger?
« Reply #5 on: 08/11/2008 15:29:13 »
Yes, Micky - thank you for your way out idea.
 

Offline iko

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How does stretching wire make it stronger?
« Reply #6 on: 08/11/2008 16:32:18 »
Interestingly enough, collagen fibers in tendons, fasciae and "connective" tissue
seem to adopt the principle of the wire rope at molecular level:




« Last Edit: 08/11/2008 16:38:24 by iko »
 

Offline Alandriel

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How does stretching wire make it stronger?
« Reply #7 on: 08/11/2008 22:13:04 »
Interesting.

Engineering imitates nature (yet again!)
but not in this case I think, since back in the 1830's when Whilhelm Albert invented
the modern wire rope we knew this much about anatomy.




Yes - I'm guilty. I looked it up    (<-- I like this guy!)



but only because I find wire rope fascinating and totally scarey........




        Aiguille du Midi - Chamonix



Some trivia:

The Aiguille du Midi lift was first thought of by two Swiss engineers in 1905. Their plan was to link the hamlet of Les Pelerins with the summit of l'Aiguille du Midi. The project met technical problems and was abandoned. Four years later a French company, Funicular Railways, made a new attempt and the first section Les Pelerins - La Para was opened in 1924.

The second section La Para - Les Glaciers was completed three years later. It was then the highest cable car in the world. With the outbreak of the WWII and the opening of the Planpraz to Brevent cable car, the popularity of the Aiguille du Midi diminished and it was closed in 1951. An Italian engineer Count Dino Lora Totino was called in to rebuild and extend the cable car.

Four years and a lot of hard work later, the new Aiguille du Midi cable car was finally completed. It was entirely renovated in 1991.


.... but I still look at cables nervously....
« Last Edit: 08/11/2008 22:14:41 by Alandriel »
 

Offline DoctorBeaver

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How does stretching wire make it stronger?
« Reply #8 on: 08/11/2008 22:32:52 »
I do not like cable cars. They scare the hell out of me.
 

Offline iko

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How does stretching wire make it stronger?
« Reply #9 on: 29/11/2008 09:12:16 »
I do not like cable cars. They scare the hell out of me.

...but without a rope is much more scaring!!!  ;D ;D  :o



« Last Edit: 29/11/2008 09:14:20 by iko »
 

Offline yor_on

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How does stretching wire make it stronger?
« Reply #10 on: 02/12/2008 13:23:19 »
Should I understand 'work hardening' as straining the cable strands to the point just before they breaks?
And that this 'strain field dislocation' will allow them to keep their 'form' not tangling up?

But when you stress a metal you weaken it, don't you.
So testing its tensile strength may keep its fibers/threads 'untangled' afterwards but i don't see how it can make it 'stronger'?

I think it's done just to make the cables to behave in a more 'predictive' way before breaking, and that it don't 'strengthen' anything.

Or?

---
Maybe it does as a 'unified' breaking point will allow the cable to become 'stronger' as all strands will behave the same way?

Btw: Iko, a very cool link that one.
I like everything 'marine' and ropes is definitely one:)
« Last Edit: 02/12/2008 13:36:40 by yor_on »
 

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How does stretching wire make it stronger?
« Reply #10 on: 02/12/2008 13:23:19 »

 

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