Whilst looking to make a number of additions and improvements to my weapon raws, I decided to make an axe with some armor penetrating potential. After the crescent-shaped axes used in the later middle ages to counter the much improved armor of the time.
Lots and lots of arena testing later, I found out that the contact area required for a weapon to penetrate armor made of the same material -with a velocity multiplier of 2000, size of 650 and an accomplished axeman- is about 90. The vanilla battleaxe has a contact area of 40000.
The funny thing is also, this contact area of 90 still lets me sever limbs. Only upper legs remained impervious. Against an unarmored creature, I was only unable to sever the lower body. Sounds about right for an axe.
I tested this with a creature made for the purpose, a human with all atribute variation removed. Each one is completely identical. I made one variation that drops unconcious upon spawning, allowing me to hit it with maximum damage hits without it being all annoying and hitting me back.
A few other things I found are: Penetration size (the number after contact area) has no influence on armor penetration. Armor strength is also determined by the size of the bodypart being hit. Against an uncouncious creature, the axe either severs a bodypart in only a few hits, or only causes bruises no matter how often I hit it. Regular combat is less... binary, but I could still sever an armored limb in one strike if lucky enough.
Possibly reducing the penetration size could reduce the overly sever-y bit.
Edit: weapon size also does not seem to influence armor penetration. Note that I am only using a single layer of full coverage, non-chainmail armor. No clothes or anything.... actualy, now that I think about it the upper legs are protected by both the body and leg armor. This may explain why they so difficult to sever.
Just putting it out here for anyone trying to do something similar. Any further insights, mistakes in my testing method or other comment is welcome.