In the back of Character Law, theres an option rule on damage to armour.
It has rules on how many 'hits' certain armours can take (based on materials, bonuses and prices), how many hits are taken off the total based on the amount of hits and crit severity a PC takes and also, how much it costs to fix the armour (with different modifiers for the percentage damage it's taken). There comes a point where you can only fix so much until you need to take it to a professional for servicing.
I use an excel spreadsheet for the character sheets and I added a page in there to work out the above per character and they just tick the boxes as the armour's taken more and more damage and then rubs them out if they've successfully used their leather/metal crafts roll (or taken it to the pros for a cost factor that's also in the optional armour rules).
Definitely a book to purchase for optional rules on magic at the back too as well as loads of Talents, Flaws, Status, Wealth, Items, new TPs and new Races!