The Mechanics of Fingernail Cracking

I have managed to further savage a couple of my fingernails and toenails lately, so that made me wonder about their mechanical and growth properties (and, more particularly, if I have done additional permanent damage to them). I hadn't gotten around to googling this yet, but todat's issue of mini-AIR has helped answer one of my questions. (I'm actually pretty amused that an issue of mini-AIR, meant to make us laugh and then to make us think, has managed to do that. It doesn't usually have blurbs about things in which I already knew I was interested. Now I can just cross my fingers and hope that time does a bit of desavaging...)