Polycrystalline materials: deformability
In a polycrystalline material with a face-centered cubic structure there are 12 sliding systems that allow for easy, low load motion of the dislocations. These materials are therefore easily deformable as a result of plastic processing (rolling, drawing, extrusion).
Rolling involves the passage of a metal sheet between two rolling rolls in order to thin its section. In the case of drawing and extrusion, a metal bar is forced through a nozzle to reduce its diameter: the difference between the two mechanisms is that in extrusion the bar is pushed through the nozzle, while in drawing the bar is pulled. The effect is the same.
The phenomenon of the accumulation of dislocations.

Suppose you load the material (i.e. subject it to a stress) and reach the elastic limit (point A, i.e. the yield strength). The moment the yield strength is exceeded, plastic deformation occurs.
In the top right-hand picture, we are in the elastic regime: once the applied load is removed, the deformation is recovered.
In the lower left-hand corner, on the other hand, we are in the plastic regime: once the elastic limit load has been exceeded and the load removed, irreversible residual epsilon deformation remains. The higher the load is increased after yielding, the more significant the residual deformation will be (image bottom right).
It is often difficult to determine the yield load, so a conventional yield load is defined, corresponding to a permanent deformation of 0.2%. This can be obtained by analysing the curve.
Note that the load at the elastic limit is different from the yield load: the former is the load at the end of the elastic regime, then there is a transition zone and finally the onset of plastic deformation.