While holding an upgraded melee weapon find another melee weapon on the ground.
Hold triangle to swap weapons. Hold triangle again to pick up the upgraded melee weapon.
You now have materials to make a shiv or a duplicate upgraded melee weapon.
This can be repeated as many times as desired.
This can only be done on the un-patched version of the game.
By repeatedly replacing an upgraded melee weapon with a non-upgraded weapon, the material used to create the upgraded weapon will appear back in the inventory.
In the updated patched version when attempting this glitch/cheat, you will see the items appear in the inventory, but then they will almost immediately disappear.
Were is the science building