Thank you all for your responses so far. I realize what I'm asking you is complicated, and I appreciate the time you've taken to provide further insight into the situation. While some, I've thought about but forgot to mention, others are ones I haven't considered. If an exact function for damage isn't readily obtainable, even an approximation would suffice. I apologize in advance for this rather long post.
I see answers encompassing swing method (positioning, angle, follow-through), defense (armor, density), weapon type, and accuracy.
I feel there's a need to elaborate further on my situation, so that we can keep the discussion specific and not overextend ourselves. The game will be essentially a mix between rougelikes such as nethack, and the turn based battling system found in games like KQ and games made with RPG Maker XP. Players will have attributes such as strength, dexterity, constitution, intelligence, and wisdom, as well as skills.
In an effort to simplify attack calculations, I've divided attacks into various parts:
accuracy -- Chance to hit, and if hit, chance to land a critical hit. This will be positively affected by increase in dexterity, and/or decrease in effective weight which describes how heavy the item feels based on player strength (inversely related to strength; ex a 16kg club may have an effective weight of 16kg for someone with 10 str, but would have effective weight of 8kg for someone w/ 20 str.).
attack bonuses / penalties -- modifiers to attack damage based on weapon type (flail, blunt, cutting, piercing, stabbing, swinging) and enemy's armor type (platemail, ringmail, shield, ect). (Certain weapon types are more or less effective against certain armor types. Ring mail may protect against blades, but won't be very effective vs. clubs.)
unmodified damage -- Damage an attack would cause prior to being submitted to attack bonuses/penalties and prior to accounting for defense's damage reduction. This is the portion I'm seeking help for. The KE formula will likely play a role here as will other factors. Strength, dexterity, arm mass and length, weapon mass and distance from pivoting point (shoulder) of weapon's center of balance, weapon velocity (for thrust) and angular velocity (for swing), and moment of Inertia (for swing) will play a positive roll in calculating this value. Attack area (the larger the area, the more the attack is distributed, and less damage is inflicted), impact time (time it takes weapon to stop moving when swinging/thrusting. The shorter the time in which the momentum changes to 0, the greater the counter-force that the target must exert to stop the weapon, and so, the greater the damage.)
Defense / Damage Reduction -- The amount and/or factor by which the unmodified damage is reduced due to the target's armor/defense rating. I'll be using a simple formula for this. Different equipment will provide a AC value. A damage percentage reduction formula will be devised with lower and upper limits of 0 and 1 respectively. Ex. DMG_REDUCT = ((AC / AC + 40)). finalAttack = (unmodified damage * (bonuses/penalties multipliers) - AC*(DMG_REDUCT) ) * (1 - DMG_REDUCT). So, if the unmodified damage is 60 and the AC is 10, the final damage would be (50 - 10 * (10/50) ) * (1 - (10/50)) = 48 * .8 = 38.4
Dodge/Evade -- chance to evade an attack. This will largely be determined by quickness (a factor derived from dexterity).
Because I'm choosing to deal with defense separately, it might be acceptable to consider the target to be unarmored. It could be considered to be the flesh of some animal (pig, cow, seal, ect) (though I realize the presence of bones may complicate this, consider just boneless flesh.) Or perhaps even imagine the target to be a large block of material (ex. clay) of some density p. (let me know what other factors may be needed here)
Though damage might not be properly defined, consider it to increase as the square of the penetration distance through a material increase. Ex. if damage is 8 for an attack that causes a gash 1 cm wide, 4 cm long, and 2 cm deep, it will be 32 for a gash 1cm wide, 4cm long and 4 cm deep.... so as the penetration distance doubles, the damage quadruples.
Anyhow, my question regarding attack damage formula can be regarded as what formula (or approximation) would represent the penetration of a melee weapon through a block of material of uniform consistency? I'm thinking KE, momentum, time it takes for momentum to go from impact momentum to 0, impact area, impact force may be things to look at when considering this.
