A few questions about twisting objects

[Macroer]

Hello everyone, i'm not really sure if this is the proper place to ask these kind of questions, but here it goes:

Twisting  seems to break everything from tree branches to iron wire:

Could you twist a rock until it breaks in half using some sort of machinery? What would the cross-section even look like?

[Strange]

Some materials (e.g brittle rocks) will shear before they can be distorted by twisting.

I wonder what the technical term in materials science is for deformation caused by twisting?

I wonder if there are rocks that are malleable enough to be twisted without shearing or shattering?

Edited April 28, 2018 by Strange

[Macroer]

10 minutes ago, Strange said:

Some materials (e.g brittle rocks) will shear before they can be distorted by twisting.

I wonder what the technical term in materials science is for deformation caused by twisting?

I wonder if there are rocks that are malleable enough to be twisted without shearing or shattering?

I found this wikipedia article describing twisting on atomic level but i don't understand enough of it to apply it to twisting a rock for example:

https://en.wikipedia.org/wiki/Molecular_vibration

It looks like the material that gets twisted gets denser and denser until it breaks. If i think about twisting a dishcloth

Edited April 28, 2018 by Macroer

[Bender]

1 hour ago, Macroer said:

Hello everyone, i'm not really sure if this is the proper place to ask these kind of questions, but here it goes:

Twisting  seems to break everything from tree branches to iron wire:

Could you twist a rock until it breaks in half using some sort of machinery? What would the cross-section even look like?

There is nothing special about twisting. Pulling breaks everything. Shearing breaks everything. Squashing breaks anything...

Twisting is nothing but shearing, but around an axis. You'll notice the fractures always spiral in a 45 degree angle.

[studiot]

1 hour ago, Strange said:

I wonder what the technical term in materials science is for deformation caused by twisting?

At molecular level there is something called a screw dislocation in materials science theory.

https://www.google.com/search?q=screw+dislocation&ie=utf-8&oe=utf-8&client=firefox-b

At a larger scale it is responsible for the ocean gyres, due to the Coriolis force.

 

1 hour ago, Strange said:

I wonder if there are rocks that are malleable enough to be twisted without shearing or shattering?

Yes, this is a plastic behaviour and is used in soil mechanics to determine what is known as the Atterberg limits.

https://www.google.com/search?client=firefox-b&ei=2GDkWqXwOcmZgAbE7LSAAw&q=atterberg+test&oq=atterberg+&gs_l=psy-ab.1.0.0l10.85674.87388.0.90364.10.10.0.0.0.0.178.1110.0j8.8.0.foo%2Ckpnr%3D200%2Ccfro%3D1.3..0...1.1.64.psy-ab..2.8.1102...0i67k1j0i131k1j0i131i46k1j46i131k1j0i10k1.0.l92DHmCneDg

The simplest form is rolling a plastic material like dough or soil or plasticine between the fingers.

1 hour ago, Macroer said:

Twisting  seems to break everything from tree branches to iron wire:

Yes indeed torsion can be very destructive.

This is often because very high stresses can be developed when it is combined with other forms of stress, which direct, shear and bending.

I am going to be proposing this as a possible reason for the recent Florida Bridge collapse in the current thread on that subject here.

[Strange]

1 minute ago, studiot said:

Yes indeed torsion can be very destructive.

Torsion. That’s the word I was trying to think of.

[Macroer]

Thanks, now i know the correct words to ask Google. A wild thought: black holes also seem like some sort of torsion action

[Strange]

11 minutes ago, Macroer said:

A wild thought: black holes also seem like some sort of torsion action

There is an extension to Einstein's theory called Einstein-Cartan theory which includes torsion; this (apparently) removes singularities from black holes and the early universe. (And that is all I know about it!)

[studiot]

Torsion is the effect produced by two opposing (but separated) couples.

A single couple will produce rotation.

This similar to two opposing (but separated) forces combining to produce a couple.

[Bender]

4 hours ago, studiot said:

Yes indeed torsion can be very destructive.

Skiers know all about it. Spiral fractures can be nasty.