Odd Blade Question

[SkepJ]

Hi everybody, new here. I have a very unusual question. It's for a hard science fiction universe I'm slowly working on. How thin would a blade have to be to cut through metals, rock etc. like a hot wire through butter? The SF blade in question is 1cm wide, 30cm long and ?um-mm thick. The edge itself is 2nm(possibly thinner, down to 0.5nm) thick. Being hard science fiction this would have to be possible in reality, just not with current technology levels. The blade is supposed to be made of a very strong form of carbon called nanotubes and held together with a resin. Basically the future version of carbon fiber composites. Thanks for the help.

 

[Nixelplix]

Why don't you use a mono-molecular whip instead? Or a lightsaber? Or a vibro-blade created out of forcefields? There might be copywrite infringements, but you can change the weapon's descriptions a little. Its science fiction, anyway. If you really want to have "hard" science fiction, the technology you describe must be somewhat plausable by today's technological standards. I don't think that anything with an edge 0.5-2 nm thick would hold up to being swung through the air, let alone cutting through anything. It would have to be supported by an energy field of some type. And then there goes your "hard" science right out the window. I think that science fiction stories benefit less from the imaginary technologies they describe than they do to the social/cultural issues they explore, anyway.

 

[SkepJ]

Why don't you use a mono-molecular whip instead? Or a lightsaber? Or a vibro-blade created out of forcefields? There might be copywrite infringements, but you can change the weapon's descriptions a little. Its science fiction, anyway. If you really want to have "hard" science fiction, the technology you describe must be somewhat plausable by today's technological standards. I don't think that anything with an edge 0.5-2 nm thick would hold up to being swung through the air, let alone cutting through anything. It would have to be supported by an energy field of some type. And then there goes your "hard" science right out the window. I think that science fiction stories benefit less from the imaginary technologies they describe than they do to the social/cultural issues they explore, anyway.

But I'm wanting my own thing and being realistic about it. Also these blades are supposed to be a body part of an animal. Technological isn't really an option here, it has to be something that could be evolved. Carbon nanotubes have a theoretical tensile strength of 200 gigapascals and a Youngs Modulus of 1-5.5 terapascals. If this is enough for a workable blade I do not know. The original thickness I was going for was 10um; but even this would flop around like a ribbon. It must be thicker than this, to where it doesn't flop anymore than a kitchen knife.

 

[Nixelplix]

I think a more plausable explanation would be to have thicker, tough claws that are naturally sharper than a razor-- say like as sharp as a flake of obsidian-- but still extreemly strong, and back that up with exceptional muscular strength. This might not cut through steel like butter, but it would still really be able to tear ***t up.

 

[SkepJ]

Could work. Obsidian is sharp to one or a few molecules IIRC. A nanotube edge on a nanotube composite claw as thick as a aluminum can's walls are could work, maybe. Aluminum cans are about 0.0508 mm thick. Perhaps this thickness would be stiff enough.

 

[airyq]

If I am not mistaken, the cutting edge has to be harder that the substance being cut for a knife to work. Notwithstanding that carbon nanotubes may be very tough, if they are not harder than rock/metal, they may not cut through. The nanotubes with their toughness would survive being repeatedly swiped againt the rock/metal but ultimately would not cut through.

cf. Marvel's Wolverine where the adamantium inner skeleton/claws is said to be an extremely strong metal, thus allowing the Wolverine to cut through any thing. In our common daily experience, metals are stronger than most materials and it is therefore believable to the average person that a fictitious metal called adamantium is able to cut through any thing.

But with your stated intention to stay close to science as we know today, carbon nanotubes may just not be good blade material.

I may well be wrong on the physical properties of carbon nanotubes and I am not trying to be a pri-ck, just entering into a bit of hopefully constructive discussion.

 

[basjoo]

I think nixelplix is on a more plausible track. This doesn't have to be a carbon-based life form. Silicone based or some other element might open up a lot of possibilities.

 

[Gollnick]

The thinner the better. If you can get 'er down to a single atom's thickness, that would be the best.

 

[HighTen]

I'm in to science fiction a lot too. I don't try to make my own up, I just enjoy the stuff others have thought up. Anyway, last summer I read a great book with an idea like yours at the center of the story. It was called The Descent of Anansi. The authors were Larry Niven and Steven Barnes and it was published in 1982. It was a really great story and that's why it popped into my head when I started to read this thread. Check this book out, you'll enjoy it. I guarantee!

 

[underaged!]

The thinner the better. If you can get 'er down to a single atom's thickness, that would be the best.

Yes, and have the atoms lined up and held together with an electric field, similar to that of the movie, Xchange (rated R-lots of sex, I was thrown off by it, I couldn't tell if it was a porn flick or just a movie with lots of humpin).

Anyway, they main character bought this thing from a spy shop. It was a short cylindrical metal object. There was a tab or something on it. When he pulled the tab, the space between the tab thing and the other thingie, could cut steel, as you described. And it worked kind of like how I described.

The side kick,lady person, ended up chopping off the main character's fingers, when they were in hand cuffs and she attempted to cut them off with it.

 

[Esav Benyamin]

I don't see how it would work with the science we know now. What you're describing IS like carbon fiber, or composites like G-10. They get stiff enough to stab with but wear against anything reasonably hard and the edge will not cut well.

You might have a creature that grows extensions like this within which harder materials were biologically concentrated, like quartz crystals or iron-with-carbon, which is steel. But neither quartz nor untreated steel would cut real well, either, and certainly not in wire-thin concentrations.

Even diamond-tipped drills wear out. If you posit a creature that grows quartz-impregnated claws that continue to grow, as the tip wears out, a new sharpened/polished tip is produced by the friction that wore it down. But slashing cleanly through rock and metal seems to be pushing it past hard-science reality.

 

[dialex]

Welcome to the Forum. While I can't tel you the thickness of this blade in mm, I'd like to share some things I read, maybe you can find something useful.
First, you are saying that these nanotube blades are part of an animal of some kind. Since they can cut through rock, steel aso, wouldn't be the risk to cut the animal itself? You should imagine a way to keep those things retracted in some very precise way, so they won't touch the flesh (or whatever this thing has) during various movements.

Second, I read some time ago a book called "The Abbey". There's this guy that uses a saber (well, sorta) made out of a liquid metal which normally is stored somewhere under the skin of his forearm, and there's only a scar showing that he has something there. The liquid metal (named "accun", BTW), gets "stiff" under a small electric field (generated by the human body itself). With training, you can shape this blade in various lengths and thicknesses (up to a few atoms, therefore it can cut lots of things).
I don't suggest to use the same approach, it's just for your info, to see what others conceived.

Good luck with your writing and let us know when it's ready

 

[SkepJ]

Already thought of a way to keep the animal safe from its own blade claws. They are out on a modified digit on the side of their arm that can only rotate forwards and backwards; flicking the blade forward to where it can be used and back to where it's parallel with the arm.

The problem with having an entire blade just a few atoms thick is it's insanely flexible. Have you ever handled gold leaf? It's not even close to this thin and is very very very very flexible. True it's gold and thus is really soft but any material save possibly neutronium from neutron stars would bend all over the place this thin. Electric fields holding the blade stiff are out, it has to be something biology could have.

 

[FoxholeAtheist]

Highten, the monomolecular wire they mentioned in Descent was used MUCH earlier by Niven in many of his Known Space books. Ringworld, for one, features a sword that contains a small spool of monomolecular wire and a tiny stasis field generator. You can extend the wire to the length you desire (it has a little red ball on the end so that you can tell where the blade is), thus the name "variable sword".

SkepJ, since you're talking about this being hard SF, and this blade having evolved on an animal, I'm assuming you've already thought about the evolutionary arms race necessary for this kind of thing to come about, right? You'll have to have another type of critter (or something) available for your slicer to sharpen his claws on...

 

[Nixelplix]

this blade having evolved on an animal, I'm assuming you've already thought about the evolutionary arms race necessary for this kind of thing to come about, right? You'll have to have another type of critter (or something) available for your slicer to sharpen his claws on...

That makes me think of the aliens in the Aliens series. How the heck did those guys evolve, with their parasitic larval stage, molecular acid blood, and exoskelatal armor plating, and mean inner jaw set, and sharp claws and sharp tail and just going to rip you to shreads or genrally make the rest of your short life miserable kind of guys. I think I saw something about it in some Aliens comics back in the 80's, but I can't really remember it.

 

[SkepJ]

If I am not mistaken, the cutting edge has to be harder that the substance being cut for a knife to work. Notwithstanding that carbon nanotubes may be very tough, if they are not harder than rock/metal, they may not cut through. The nanotubes with their toughness would survive being repeatedly swiped againt the rock/metal but ultimately would not cut through.

Well I picked carbon nanotubes because they are the current strongest material known. They are completely composed of a type of chemical bond called sp2 which is very very strong. Diamonds are held together with weaker sp3 bonds. The reason for the edge being a single nanotube running up the length of the blade is because a monomolecule edge would be much more durable than one made of billions of crystals.

I may just have to go with normal thickness claws with a monomolecular edge like Nixelplix suggested. What could such claws be made of that would hold up? Obsidian dulls even as hard as it is. A glass claw would break too easily also.

 

[HoB]

Well a well sharpened regular blade has an edge of about 1 micron thick, so I would guess it would have to be less than that. But the real problem is not the edge but the thickness of the blade itself. If the blade itself is much thicker than a few nanometers, it will have to push the material apart whether it is cut or not. So like hot knife thru butter will probalby not work no matter what you propose, execept if you melt the rock (like butter). In terms of claws a la Wolverine: there are certain ceramics that are around 9 on the Moos scale but exhibit a surprising flexibility (toughness I don't know) also there was talk about a Fluor-Diamond film a few years ago, where they trapped fluorine atoms inside of Bucky balls and were able to make a film of up to 1mm thickness. The film on a substrate support was supposed to be 10 deg bendable and the film was supposed to be substantially harder than diamond. Theoretical calculations predicted that Nitrogen-Diamond was supposed to be even harder, but they failed to make it. Hope that helps.

 

[SkepJ]

Well a well sharpened regular blade has an edge of about 1 micron thick, so I would guess it would have to be less than that. But the real problem is not the edge but the thickness of the blade itself. If the blade itself is much thicker than a few nanometers, it will have to push the material apart whether it is cut or not. So like hot knife thru butter will probalby not work no matter what you propose, execept if you melt the rock (like butter). In terms of claws a la Wolverine: there are certain ceramics that are around 9 on the Moos scale but exhibit a surprising flexibility (toughness I don't know) also there was talk about a Fluor-Diamond film a few years ago, where they trapped fluorine atoms inside of Bucky balls and were able to make a film of up to 1mm thickness. The film on a substrate support was supposed to be 10 deg bendable and the film was supposed to be substantially harder than diamond. Theoretical calculations predicted that Nitrogen-Diamond was supposed to be even harder, but they failed to make it. Hope that helps.

Well it wouldn't have to be totally effortless. A kilo of pressure on the blade to make it cut through hardened steel would be passible to me. Could a blade the thickness of a soda can or even photographic film do this? Putting enough pressure on a small area is what cutting is all about. One wouldn't want to wear high heeled woman's shoes walking on thin ice. Snow shoes or not doing it at all would be much better.

 

[Bobwhite]

I can't tell you anything about how to do what you are asking, but I am interested in reading your story when it is done. And I don't care if the science is fudged a bit personally, but I respect your wanting it to be as sound as possible. Let us know more about the story if you care to, You got my interest peaked.

 

[SkepJ]

I can't tell you anything about how to do what you are asking, but I am interested in reading your story when it is done. And I don't care if the science is fudged a bit personally, but I respect your wanting it to be as sound as possible. Let us know more about the story if you care to, You got my interest peaked.

If it ever becomes a book will do. Also bumping for more input.