How do the properties of density, sharpness, brittleness of a material impact on the usability and the design of weapons.

Would it cause weapons to be designed vastly different or would it make normal weapons more effective?

The density of steel "ranges between 7,750 and 8,050 kg/m³". For diamond it is just 3,500 to 3,530 kg/m³. (just as an example for vastly different densities)

If we were to create a regular long-sword or katana out of a material about half the weight as steel, but with similar properties regarding sharpness and brittleness, would it be as useful? What if the weight was even lower than that? It would have a weaker impact for sure, but it could be swung faster, too.

Now what if we improve the sharpness? If a blade was significantly lighter, but also sharper, it would be a lot easier to use against "soft" targets. But the light weight would probably make it useless against "hard" targets if it can't cut through the hard layers.

What kind of new designs of weapons (all kinds of weapons) and armor would be possible and useful if such a material existed?

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    $\begingroup$ "sharpness and hardness" - what about brittleness? Elasticity? If you mean "everything is exactly the same, just lighter" then make it clear that you meant every physical property. Because diamond armor was already shown to make little sense, and reasons given are also valid for swords. $\endgroup$ – Mołot Oct 24 '17 at 9:32
  • $\begingroup$ i'm gonna include this. That's what i meant by hardness, mostly. But i didn't know the right word brittleness. Thanks! $\endgroup$ – ArtificialSoul Oct 24 '17 at 9:34
  • $\begingroup$ A full answer is too hard to formulate this morning so I'll paraphrase heavily: unless you go to extremes of sharpness i.e. blades of mono-atomic thickness weight is actually your friend. $\endgroup$ – Ash Oct 24 '17 at 11:21
  • $\begingroup$ Keep in mind that materials like these will also have an impact on the armor design as well. $\endgroup$ – xpy Oct 24 '17 at 14:12
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    $\begingroup$ @ArtificialSoul I voted it closed for that reason, that bottom bolded question clearly makes this question WAY to broad $\endgroup$ – anon Nov 9 '17 at 23:18

If you ever cut your finger with a sheet of paper, you will have no problem in agreeing that paper is pretty sharp. Still nobody has ever started a war with an army equipped with A4 sheets...

If you are going for cutting weapons (for things like an hammer or a mace you won't rely on sharpness at all) you will need mass to support the hit by transferring momentum. But you will need also less mass to make the movement of the sword not too cumbersome.

In short, you need a tradeoff between ability to deal the desired amount of damage and ability of waving the weapon around.

Mind that there is no unique solution to this problem: two hands sword sacrificed mobility for momentum, while katana were relying more on the cutting and agility than on the momentum. You'll guess that it depends on who is your enemy: by the time a warrior with a two handed sword has lifted it, a samurai would have already chopped his arms away. But to stop the inertia of a charging enemy a katana would do almost nothing with respect to a two handed sword.

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    $\begingroup$ A great sword or broadsword with half the weight would be pointless, a lance or halberd with half the weight would be pointy... +1 $\endgroup$ – Joe Bloggs Oct 24 '17 at 10:19
  • $\begingroup$ Yeah, that's why i used a regular longsword as an example. The momentum would be significantly reduced and it would lose a majority of it's damage potential, but my questions is also regarding cases where it would improve the weapons (maybe daggers or other smaller hand weapons) and what new possibilites would arise in weapon design if such a material existed. $\endgroup$ – ArtificialSoul Oct 24 '17 at 10:33
  • $\begingroup$ @LDutch What about an army of lawyers? $\endgroup$ – Phil M Oct 24 '17 at 15:51
  • $\begingroup$ @JoeBloggs consider that in the case of the lance, the weight of the lance is nothing compared to the momentum of horse and rider behind it. Polearm needs some heft; consider that we use lightweight rattan weapons in training to avoid injury, the which is contraindicated during real combat. $\endgroup$ – akaioi Oct 24 '17 at 17:57
  • $\begingroup$ @Akaloi: that’s why a lighter lance is better: lighter weight = longer reach or greater accuracy. Perhaps Pike would have been a better choice for that particular pun than halberd, though a lighter weight of handle could still be advantageous if you keep the head weight the same. $\endgroup$ – Joe Bloggs Oct 24 '17 at 18:30

Weapons and armour are a constant game of one-upmanship, but they are closely related.

Each must be suitable for the situation and the opponent you're facing.

  • European weapons, such as the broadsword, were designed for dealing with relatively heavily armoured opponents.
  • Japanese weapons, such as the katana, were designed for relatively lightly armoured opponents.

In the case of the katana, speed and cutting edge were primary. If you could create a lighter, tougher blade which held a very good cutting edge then that may be advantageous to the wielder. In contrast, one of the defining characteristics of a long sword is its weight. To make it considerably lighter, even while maintaining all other characteristics may make it an unsuitable weapon for the situation.

Once firearms made heavy armour obsolete then lighter, faster edged weapons returned to the European theatre. There may be a place for your weapon with late cavalry units.

  • $\begingroup$ <sigh> A typical longsword weighs about three pounds. The heaviest ones go up to four, and the lightest ones go down to about two and a half. The heaviest katanas are right around three pounds, and the lightest ones are about two and a half. A typical katana weighs less than a typical longsword by about the weight of the beef patty in a 1/4 lb burger... A typical smallsword (what eventually became popular after firearms) weighs between 1 and 1.5 pounds. $\endgroup$ – Perkins Oct 24 '17 at 16:45
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    $\begingroup$ @Perkins, even a warhammer was only up to 4lbs, don't underestimate the importance of small changes in weight. $\endgroup$ – Separatrix Oct 25 '17 at 7:15
  • $\begingroup$ As an example, I'm a kayaker, I use Lettmann Polo LCS 70, weighing 1030g (~2.27lb), these feel very heavy compared to the 797g (~1.75lb) CPS Kinetic even though the difference is almost exactly 0.5lb. Apparently tiny differences, when applied with those leverages, are highly significant. $\endgroup$ – Separatrix Oct 25 '17 at 9:15
  • $\begingroup$ The balance of a warhammer is significantly different, and it's used in a different manner. It will be more similar to your kayak paddles. Longswords and katanas tend to be balanced just a few inches in front of the hand guard. Having used both types of sword, the curvature and handguard differences have more effect on the styles for which they're suitable than the weight difference. $\endgroup$ – Perkins Oct 26 '17 at 21:54

I have seen off and on the prospect of carbon fiber swords. Carbon fiber tennis rackets are amazing. I figured a carbon fiber sword would be super light and maneuverable.

This guy with his carbon fiber lightsaber did not seem too intimidating until this part of the video. https://youtu.be/NjnLrMkk-Tw?t=153

carbon fiber blade and some badass moves

Earlier in the video he whacks that carbon fiber blade vigorously on the ground, which I think would have shattered a tennis racquet - clearly there is more than one type of carbon fiber.

Carbon fiber knives (100%; no metal blade) are widely available. It did not seem to me that carbon fiber would keep an edge and I was right. Here is a piece of text from a merchant site: http://hiconsumption.com/2016/04/best-carbon-fiber-edc-knives/.

Knives can even be made wholly out of carbon fiber, which allows for blades that can be easily honed with a piece of sandpaper. They won’t retain an edge for long, but for quick stabbing work or a few single slashes, such dark daggers are ideal.

Not keeping an edge is a deal killer for a chef knife but not a sword. I am certain that people who relied on the sharpness of their swords were not using them like machetes. They sharpened them and then sheathed them. After they used them, they cleaned them and sharpened them again before putting them away. The swords came out if there was someone to kill. If rapid blunting were a big problem, one could attach a thin edge of carbon steel - maybe even in small (replaceable) sections like a utility knife, to still allow flex of the sword.

A quick perusal of youtube finds plenty of videos showing how sharp these carbon fiber knives are. Sharp.

As previously noted the use of this light sword would not be a club with an edge to batter people down. It would be a thrusting, slashing weapon.


There are a number of competing factors at work here. Ultimately it is a matter of how much force can be applied in how small an area. Being more massive increases the amount of kinetic energy that can be delivered in to the target, but at the expense of making the weapon more unwieldy. Making the weapon sharper reduces the area over which the force is applied increasing the pressure at the point of contact, but at the expense of making the edge vulnerable to damage.

Steel is actually a very good material for making swords with especialy some tool steel as it can be heat treated and tempered. You can make a more durable sword out of titanium but it will be considerably softer than steel and you cannot temper it.

Making a lighter sword would theoretically allow it to be moved faster, but I doubt the increase in speed would make up for the decrease in weight, although it would depend on the detailed circumstances in which you were using it.

One key property is the sharpness and the durability of that sharpness. A material that could be sharpened to a few atoms thick at the blade edge would be a fearsome weapon if that sharpness could be maintained – which with current technology it could not.

I am sure that there’s a lot of scope for increasing sword performance using modern composite materials in conjunction with more traditional materials as well as specialist high performance coatings, however unfortunately for swords, modern firearms have pushed sword development technology into the doldrums.

  • $\begingroup$ Titanium is actually only about 95% as strong as steel. The only reason anyone uses it at current prices is because it's right around 50% of the weight. You can't heat treat and temper it, but that in no way affects the quality of the finished product, merely the difficulty of the manufacturing process as it must be hardened by alloy composition and worked at full hardness, and variations in hardness must be done by varying the alloy. Much more difficult, but not at all impossible. $\endgroup$ – Perkins Oct 24 '17 at 16:50
  • $\begingroup$ Yes although the question is a little complex as it is not clear which steel @Perkins alloys are being compared with which Titanium alloys. I suspect the most commonly used alloy of Titanium (6al4v) is significantly stronger than the most commonly used steels, but the strongest steel alloys are stronger than the strongest Titanium alloys. But I stand to be corrected if anyone knows better. $\endgroup$ – Slarty Oct 24 '17 at 17:57

If you wanted to go into the realm of science fiction, you wouldn't go past Monomolecular wire.

It's a strand of a virtually unbreakable filament only a few atoms thick that can be used in a sword or a whip. Since it's so thin, it's like a cheese slicer on steroids. It can cut through almost anything with little effort.


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