There are rules in GURPS for armor taking damage after absorbing a specific amount based on damage type(1 point of DR lost per 10 points of damage absorbed normally). There's also armor parts and customization armor weight. Unfortunately, by the time most armor would be worn through the wearer would be very dead.
Pathfinder has a feat called Fortified Armor Training, I believe, located in Ultimate Combat, which lets you stop a critical hit by breaking your armor instead... but that's hardly a whole system. I don't know if there's a system out there that's quite what you're looking for, but it does sound like it would be easy to house rule, as others have said.
I've actually made up a basic system for this thanks to that feat. Though it hasn't been play tested.
Armor and clothing have different levels of coverage. For both this is determined by the AC bonus of the item(normal clothing is considered +0). Certain events cause AC damage which lowers the maximum bonus.
When an item has half of its AC bonus removed it gains the broken condition and no longer is considered to be covering any important parts of the person. Any additional instances of AC damage destroy the item. Regular clothing is instantly destroyed if it takes AC damage.
The following events cause AC damage.
- Critical Hits: 1 point of AC damage per crit multiplier on the attack(2 for x2, 3 for x3, etc). The critical hit causes normal damage rather than extra damage.
- Natural 1's rolled on saving throws: Causes 1 point of AC damage if the spell would deal damage.
- Failing a physical skill check: 1 point of AC damage per 5 points of failure.
- Enemy grapple attacks: An enemy can choose to automatically deal 1 point of AC damage as a grapple attack, rather than dealing damage to the person.
By taking 1 minute, any broken armor can be re-adjusted, restoring 1 point of AC damage.
Further repairs require use of the Craft(Armor) skill, the Make Whole spell, or similar effects.