What happens when body armor expires?
For the army, the Kevlar vest is sent for reconditioning because Kevlar has a lifespan of 5 to 8 years if used appropriately. The warranty for such products are usually 3 years, at least where the contract stipulates.
Kevlar by itself has to be kept away from water and UV rays. I don’t know how we can expect soldiers to not perspire.
A contract is signed with a company to do the reconditioning of vests and/or helmets. Such vendors are usually the lowest bidder.
The whole batch of vests and helmets that have reached the lifespan are sent to them. Some of the equipment would have been worn by soldiers, others would have remained in store for its lifetime.
As long as it is kept in a cool, dry place, Kevlar should last indefinitely.
The company will then pry apart the vest and visually check the Kevlar layers. Usually, vests that have never been used before will pass visual inspection. These will be stitched back with no further repairs given.
Those that have discolouration (sweat, mud, tears, piss etc) will be taken apart, layered with new Kevlar layers, and stitched back together.
After the batch is done, they are shipped back to the armed forces as brand new (refurbished) personal armour kit.