I suppose that you can take the subject in one of two directions, depending on your motivating principles. One: You could decide that you really want to work up a simulation of the penetration ability of certain weapons against different armor types, within the context of the D&D combat system. Two: You could instead decide that your overarching goal is to give each weapon some metagame reason to be chosen by characters in different circumstances.
Having mulled it over, I think I'll have to pick option #2 as my priority. I will again point out DMG p. 9, where Gygax makes clear that for D&D, the designer is supposed to put game-design principles ahead of realism-simulation, when a choice must be made between the two ("This is not to say that where it does not interfere with the flow of the game that the highest degree of realism hasn't been attempted...") Taking this longer-view perspective, the answer will sometimes be to-hit-adjustments, and at other times be something entirely different. It will not be systematizable in a matrix of numbers.
So here is a new proposal for distinguishing between different weapon types. First of all, let me be clear that I use the variable weapon damage from Greyhawk, but ignore the separate statistics for L-size enemies (and other modifiers). Hence weapon damage follows this simple rule:
- d4: Dagger, sling.
- d6: Hand axe, mace, spear, arrow, quarrel.
- d8: Sword, battle axe, morning star, flail, pole arm, lance, pike.
- d10: Halberd, two-handed sword.
- Swords (dagger, sword, two-handed sword): Blades are light and compact. They can be easily carried in a scabbard (half encumbrance), and can stab in constricted spaces where other weapons are unusable (e.g., narrow tunnel, monster gizzard, etc.)
- Spears (spear, lance, polearm, pike): Pole weapons provide reach. The wielder gets a free attack when readied against an onrushing attacker with a shorter weapon; however, in each later round of melee they permit a free attack on the part of the enemy.
- Axes (hand axe, battle axe, halberd): Chopping weapons can sometimes cleave through heavy armor. They get a +1 to hit opponents wearing chain or plate.
- Clubs (mace, flail, morning star): Bludgeons can deliver shocks directly through plate without penetrating the armor. They get a +2 to hit opponents in plate mail.