If a small load is suspended from a wire, its length increases. When the load is removed, the wire regains its original length. But if a sufficiently large force is suspended from the wire, it is found that the wire does not regain its original length after the load is removed.
The maximum stress within which the body regains its original size and shape after the removal of deforming force is called elastic limit. If the deforming force exceeds the elastic limit, the body acquires a permanent set or deformation and is said to be overstrained.
Important Point Regarding Elastic Limit
Within the elastic limit, the stress is directly proportional to strain. Thus, within the elastic limit,
Stress ∝ Strain
or Stress = Constant × Strain
The constant of proportionality is called modulus of elasticity or coefficient of elasticity of the material. Its value depends on the nature of the material of the body and the manner in which it is deformed.