Any material has a property.When the force gradually increases from zero, the deformation is proportional to the force for a period of time.At this time, the force is slowly returned to zero, and the shape of the object will recover.
But when the force reaches a certain level, plastic deformation will occur, and the shape of the object will permanently change, and the relationship between force and deformation is no longer proportional.
In our daily life, springs and other items use the proportional part of the object. We don’t want them to undergo permanent deformation, so there is a term of deformation range. The deformation range is related to the material of the object, the geometric shape of the object, the temperature and so on.