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I'm sorry if I asked in the wrong place (it is my first ever question).

I have been thinking of a whole new system for the materials of the world, based on our periodic tables (sort of). The idea is that each one of the material has their own characteristics and behave in a specific way - which is similar to our world.

But in this world - like many others - there is war, and with war comes different weapons. The problem is that I have trouble figuring which material would make the best sword, or which one could be used as cutting tools or saws. After some thoughts, I believe that the toughness and weight of the weapon plays a role along its shape (like a thin blade of iron would cut a lot as opposed to fabrics which can't wound someone, whatever the quantity and shape). But I also know that a diamond sword would make quite a bad weapon. So I trust that there something else to take account of.

Therefore, my question is, what sort of characteristics should my materials have to describe / evaluate their potential sharpness ?

I hope I am not making a duplicate and thank you in advance for your answers.

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  • $\begingroup$ There are different types of hardness. Diamond is the most scratch-resistant material (Mohr scale). For weapons, you would need the best indentation resistance (Rockwell scale). Also, impact resistance (Izod or Charpy tests) are very important. $\endgroup$ – Alexander Jun 10 '17 at 18:15
  • $\begingroup$ Unlike daggers, swords are not necessarily very sharp. Sharpness is much more useful in a rapier than in a longsword. The material for a sword needs to be tough enough, stiff enough and heavy enough. Hardness, mostly indentation hardness, comes fourth. $\endgroup$ – AlexP Jun 10 '17 at 18:41
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Strength, hardness, and atomic pattern.

A cutting edge is basically just a thin as possible section of material to spread the forces of contact pressure out over as small an area as possible the maximizing the pressure on the material being cut.

To withstand this the edge material needs to be strong (in terms of both yield strength and ultimate strength) enough to not crack or bend when made thin. It needs to be hard (in the mohr sense) to maintain an edge otherwise the edge will just wear away. The size and purpose of the blade can change the balance between the two. small scalpel blade favor hard over strong, since it is too small to experience much bending, while a sword would need to be stronger and would have to sacrifice hardness to achieve it. g=Generally you want your edge as hard as possible but making it too hard often costs strength, this can be fine in a single use blade but completely counterproductive in anything that will see a lot of usage.

Generally you do not want your blade made of anything crystalline, an amorphous atomic pattern is ideal for making the sharpest edge, basically glasses, even steel knives try to keep the metal crystals as small as possible to get as close to a metallic glass as they can. Silica glass can make a much sharper edge than steel but is brittle so it only works if small and wears out quickly.

Diamond for instance is very hard but also very brittle making it useless for anything but the smallest of blades. It also has a regular crystal pattern limiting the geometry of the blade you can make so you cannot make it as sharp as a steel or glass blade.

There is a physics stack that explains the physics in more detail, and here is a paper on the subject.

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