Another way of looking at it is this. Just as a thought experiment. Gedanken. Though I understand I am probably not using the word exactly right (Stephen might help me here) or spelling it exactly right. I just like the word.
Anyway, what is tensile strength? Well, atoms have certain magnetic properties and under strain these magentic properties blah, blah, blah, blah, blah. Just put it in a machine and pull it and when it starts to stretch we'll say this represents yield strength. Where it breaks, tensile strength.
What is stress? Well, the atomic matrix has become distorted due to the expansion and contraction of atoms though the input of heat energy blah, blah, blah, blah, blah. Just smack a little ball (or a pyramid-or your finger) with a hammer, measure the indent (or the swelling), and say it represents stress relief. Thats what codes suggest.