Flamingknives, I appreciate that you have some materials training. Armor "strength" has always been kind of a strange term for me to understand. Strength, toughness, and hardness have very specific meanings in materials science. Strength is the amount of force to failure for a material per unit area (or the elastic strain limit as flamingknives stated). Toughness is the amount of energy that a material has absorbed at failure (obviously per unit area). And hardness, well that's a little more confusing. In my work, we're generally working with nanohardness--which is a materials resistance to plastic deformation upon nanoindentation. In a nutshell it's related to the modulus (stiffness) of a material. Hardness does relate somewhat to the toughness of a material, but not exactly. Flamingknives stated that hardness is the difference between the elastic and the ultimate stress of a material. I guess I should state that I'm generally working with biological materials, so I'm in no way a materials scientist and only understand the math at a very rudimentary level. Basically, what exactly does strength mean when one is talking about the armor plates on tanks?
Cheers,
J