I fail to see how a mace would cause any kind of structural damage to a shield. The contact surface area is too large.
the most damage that would be received would be an impression left in the wood
Physics class for the skeptical
impact works like a beating on skin hide drum
tap it with an old styled drum stick, it will play sound, no damage (mace)
stab it with a needle, damage, but it is too isolated to cause significant damage (spear)
tap it with a straight pizza cutter, the whole drum will split open (axe or any weighted weapon with a curved blade)
Surface area determines penetration (low surface area) and on the inverse determines the area of effect (high surface area)
the kinetic force is distributed at the area of destruction (which is high in blunter weapons) and if the kinetic force is distributed too spread apart it will do little or no visable damage (other than dents)
on the other hand if kinetic force is concentrated (like a knife stab) it will pierce through in an isolated area but like blunt weapons
(such as a mace) will not do much damage to the overall structure of the item