Elastic Recovery after Plastic Deformation of Metals
Metals can recover their original shape after being stretched to a certain limit, determined by the metal's yield strength. Beyond that, the metal experiences plastic deformation and cannot return to its original shape. Trying to bring the metal back to its original shape results in a decrease in its length and diameter.
Disclaimer: the scale of this Demonstration is exaggerated to show changes in the length and diameter of the cylinder and the changes sufficient for the metal to neck down and ultimately fracture.