Andy, I'm no scientist, but a lot of metals and plastics behave in this way, if you take  a piece of plastic and keep bending it eventually it will snap, is this what you are describing. I always thought that was down to stress and materials all suffered from that. Isn't there something called a plasticity index? I'm digging into very old learning here so could well be wrong. It sounds to me that that is what you are describing.

Alternatively as Copper ages it oxidises, this is a change of condition as a new compound is formed.

I could of course be barking up completely the wrong tree