OK, I did some "strength of materials" research to refresh my memory.
Here's a quote from a physics demo on stretching wires, "Review of
"Wires of the same guage, but made of different metals typically
support different loads ..... before going through the point at which
they change from being elastic to being plastic. Elastic deformation is
recoverable after the load is removed. Plastic deformation is not."
Now, a bolt is a piece of some guage wire with threads on one end and
a head on the other. So the above applies.
Elastic deformation is defined as the amount you can stretch the bolt
(wire) and have it recover its previous shape and tensile strength when
you loosen it. (Component atoms covalent orbits are deformed.)
Plastic deformation (strain force) is defined as the amount of stretch
that results in permanent deformation and loss of tensile strength. (
Component atoms slide in relation to each other.)
Ok, so when you properly torque a bolt up, you're stretching it to
somewhere in the middle of it's elasticity range. Tight enough that it
won't come loose but with some stretch left to handle the loads that
will be imposed later on. Over torque it and you've cut down the amount
of load capacity left in it for later. If you don't over torque it to
the point where you permanently stretch it, it will return to its
previous length and tensile strength when you loosen it.
With the above in mind, I suspect that, in the seminar that DLancer
attended, the example he described was one of explaining what happens if
you torque a bolt to it's strain force value and cause it to enter its
plastic condition. IOW, when it's stretched too far.