Tensil strenght and Young Modulus

[dragon]

While looking up some material for my research paper came acros this Apparently these MWNT (Multi Walled NanoTubes) had a tensile strenght of 11-63 GPa and a Youngs Modulus of 270-950GPa. I know steel has a tensile strength of 3GPa. So this material has a tensile strenght alot higher than that of steel. Also it was saying that a DWNT (Double Walled Naontube) has a Young's Modulus of 1.1TPa, and a maximum stress of 160GPa.

What exactly is Young's Modulus and is maximum stress the same tensile strenght.

The tensile strength and Young's
modulus of this layer were 11–63GPa and 270–
950GPa, respectively. Recent progress in preparing continuous
CNTs of macroscopic length makes it possible
to exploit their further applications in many cases

DWNT under axial tension using molecular
dynamics (MD) simulation. The results showed that its
Youngs modulus, ultimate stress and maximum strain
are around 1.1TPa, 160GPa and 28%

Linky

[Darth Wong]

Young's modulus is the modulus of elasticity, ie- the slope of the stress-strain curve below the elastic yield point. Tensile strength is normally the UTS, which is the stress in pure tension that a material can withstand before failure.

Shear strength is the stress that it can withstand in shear, ie- cutting. Compressive strength is the stress that it can withstand (obviously) in compression. And impact toughness is the material's performance on the Charpy impact test, where a small piece is struck by a huge hammer. There's a reason why nanotube-wankers always quote tensile strength and none of the other kinds. Nanotubes are only good in pure tension; any other direction of loading and they fold like paper.

[dragon]

Thank you very much thats what I need for my paper.

So according to NIAC (Nasa Institue for Advanced Concepts) a material with a tensile strenght of 100GPa is needed for a space elevator so the DWNT mets that criteria. However they don't address the effect of the other properties like Young's Modulus.

So this material which had the 160GPa but a Modulus of 1TPa should be more than good enough but would it be to inelastic.

[drachefly]

Note that the properties listed are for ONE carbon nanotube.

Massive problems arise when you bundle them together. IIRC, as of last year, the strongest rope we'd made from CNT was about as strong as copper. This is not very strong.

I expect this to get much higher soon; but it's a long long way from space elevator territory.

Can we do it? Divide a number with large fractional uncertainty by another number with large fractional uncertainty... and you get 'beats me'.

[Darth Wong]

I'd imagine the bundling problem probably has to do with the fact that it's almost impossible to produce a realistic condition where a material is stressed only in pure tension.

[drachefly]

For a space elevator, what do you need any other kind of strength for? It's a freaking rope!
Or are you also considering binding at the ends?

Or the part where the climber has to squeeze it to get traction to climb? Yeah, that's a tricky one. Which is why I prefer the rotavator, which needs no climber. And happens to be only 200 miles long instead of hundreds of times that.

[Darth Wong]

For a space elevator, what do you need any other kind of strength for? It's a freaking rope!

Which means that it's probably composed of lots of individual strands bundled in a helical fashion, which could produce a slightly more complex load.

Or are you also considering binding at the ends?

I would imagine there must be connections in-between as well, unless they can manufacture seamless strands which are thousands of kilometres long and there are no concerns about ever having to maintain it in a practical fashion.

[drachefly]

One seamless strand was the general idea put forth.
And if you have a slowly braided cord and pull on it, the lateral forces are tiny compared to the tension force. So even if the nanotubes lateral strength is unexceptional, I'm not too worried.


To be more specific, the Highlift Systems plan was a series of strands, each strand a web of the shape
XXXXXX
XXXXXX
XXXXXX
XXXXXX
so micrometeorites piercing it would only knock out a few cells even within the one strand.
Also, if I were doing this, I would make each web intersection exchange strands, so pierced strand would not have as long-range tension loss. I presume they also thought of this, but I can't say for sure.
The strands would just be laid alongside each other with only a minimal force keeping them together.

The main relevant force is the force per length supportable by an array of parallel tubes.
That is, if you put two tubes next to each other and then pull one one way and pull the other the other way, how much force it will take to make them move. As you make the tubes' interface longer, this force will be greater, up to some limit (at the very most, less than the tensile strength of an individual tube)
So, you want two tubes to be parallel for a great enough distance that the total force they can support is adequate to maintain the material's full capacity for tension.

The main problem is, unadorned tubes are really slippery, like graphite. So you're either going to need to go in and make them stickier (which we already know how to do, at the cost of some strength), or you're going to need to make each individual tube really long (not "all the way to the end" long, but still really long). We already have centimeter-long tubes. I don't know how much longer we can make them, but frankly I wouldn't be surprised if in twenty years we could make them kilometers long. That may be vastly excessive or not nearly enough; I don't know those numbers, and I don't know whether anyone else does either.

As for maintenance, the plan was to have a climber periodically lay down new strands and take up old ones. So the strands would be disposable, not to be maintained, like a microchip. The whole ribbon, however, would be maintained.

[Molyneux]

Young's modulus is the modulus of elasticity, ie- the slope of the stress-strain curve below the elastic yield point. Tensile strength is normally the UTS, which is the stress in pure tension that a material can withstand before failure.

Shear strength is the stress that it can withstand in shear, ie- cutting. Compressive strength is the stress that it can withstand (obviously) in compression. And impact toughness is the material's performance on the Charpy impact test, where a small piece is struck by a huge hammer. There's a reason why nanotube-wankers always quote tensile strength and none of the other kinds. Nanotubes are only good in pure tension; any other direction of loading and they fold like paper.

Gah, cursed Young's modulus...deformable materials is what put the kibosh on my ME studies (for the near future, at least)!

[dragon]

A really indepth study on how they they wanted it was done by NIAC (NASA Institute for Advanced Concepts). The idea was a bundle of 1cm carbon nanotube ribbon with interconnecting tape sandwich every 10cm.

Figure 7 of
link

[dragon]

Ok for some reason that link didn't comeout right, even though I followed the example on the FAQ page.

[Beowulf]

You have a single quote in the url. Put double quotes around the url if it doesn't come out right when previewing the post.