You mention armor will prevent damage, then you mention armor will prevent you getting one shotted by a ranger bow. What I was referring to is getting hit at 0 defense by a melee weapon which you entirely missed as I dropped a mention with strength.
A special mention is that unarmed attacks (including animal attacks presumably) will have 30% of its damage ignore your armor and deal damage to your SHP, Axe also have a 5% damage ignore as well. All other attack needs to have a larger damage than the total armor class of the target. Regardless if the target loses SHP or not, the attacker will gain one point of attack unless he/she was using a valorous strike.