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In order to evade the Writers can't do math and Sci-fi Writers have no sense of scale, I wish to use somewhat accurate models to simulate combat and injuries, that I can use to determine the power of the items and to an extent, their reputation in that world.

Things it needs to simulate:

  • A uniform way of determining the damage (force, pressure) of blunt, edged, and other weapons inflicted on the materials.

  • Optional: important modifying factors in the mechanical interaction (angle, etc...)

  • Determining an armor's defensive and other combat related properties, such as the "hit points" of the armor, weight properties, based on thickness, materials used in it, and the area it covers

What is the most accurate model that exist for simulating this (in the realm of classical physics)? If there's no such model, what models exist that cover one of these, that I could combine together?

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    $\begingroup$ This kind of modeling seems more useful for creating RPG's (specially videogame ones) than to create a sci-fi story proper. I don't think a realistic model exists for what you want. $\endgroup$
    – The Square-Cube Law
    Commented Apr 2, 2017 at 10:31
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    $\begingroup$ I don't think there is any software that could do that, but wounds have been studied for a while especially for forensics purposes. Thus, the best way to make an idea is to get a "human-like" dummy and practice on it. Another option could be to read articles about those studies. (Use Scihub) $\endgroup$
    – EngelOfChipolata
    Commented Apr 2, 2017 at 10:41
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    $\begingroup$ So remember that training and experience will probably have a far greater effect than the physics of your melee weapons. That's why spears and maces were preferred battlefield weapons over swords, etc. $\endgroup$
    – Konchog
    Commented Apr 2, 2017 at 13:30
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    $\begingroup$ @RedactedRedacted, I think you may not understand how melee actually works. If all you are wondering is what happens when you hit one material on another, you are just looking at materials science. Being thumped hard often does little damage to the armour but can easily kill the person unlucky enough to be hit. $\endgroup$
    – Konchog
    Commented Apr 2, 2017 at 13:54
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    $\begingroup$ What you seek is impossible in general. Combat probably has thousands of state variables wound up in hundreds of differential equations. However, we may be able to come up with an approach that would let you develop a system for your particular use cases. For example, you might be able to come up with a system that predicts that the aristocracy will retain control because the balance between aristocratic weapons and peasant armor gives the aristocracy free reign. You could create a system where the "best" weapons take training to use well, making them unavailable to peasants. $\endgroup$
    – Cort Ammon
    Commented Apr 2, 2017 at 15:55

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Have a look at Newton's approximation for impact depth. The approximation assumes that the impactor is blunt and moving very fast so it isn't very good for melee (or ancient missiles) but it should get you on the right track.

The approximation neglects cohesion in the body. So you will need to account for bone and armour (including clothing/cloth armour, which was worn even under metal armour) separately.

I would approach a first approximation to the problem of sharp weapon penetration as follows (with an emphasis on the injuries rather than the armour, which is more complex):

  • In the case of a missile, the speed at impact is fixed and falls due to the effects mentioned below.
  • In the case of a melee weapon, force may be applied after impact. Assume for simplicity that we can ignore this, especially since the user likely does not want to over-penetrate the target and get their weapon stuck.
  • Determine the speed lost in penetrating armour.
  • Estimate the impact depth at remaining velocity using Newton's approximation and average tissue density.
  • Determine which bones will be crossed along that path, and reduce the speed at that point based on the energy needed to break the bone. Use the medical literature. (If the weapon ricochets off the bone, the problem can of course be more complex.)
  • Recalculate the remaining impact depth after bone impact (if sufficient energy is available to pass through the bone).
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  • $\begingroup$ And where can I find informations about the cohesion of a material? $\endgroup$
    – Mephistopheles
    Commented May 21, 2017 at 10:53
  • $\begingroup$ Perhaps you can start with this lecture: youtube.com/watch?v=KXHeVM-bSjQ $\endgroup$
    – user25972
    Commented May 21, 2017 at 16:15
  • $\begingroup$ So, it's the shear modulus? $\endgroup$
    – Mephistopheles
    Commented May 21, 2017 at 16:19
  • $\begingroup$ It's the everything to do with how the material holds together. This includes cutting the different fibres in the body, which is heterogeneous. $\endgroup$
    – user25972
    Commented May 21, 2017 at 17:27

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