5: Tensile Springback

Tensile Springback occurs as atoms revert to their equilibrium positions following elastic deformation.

Mechanism of springback in elastic deformation:

  1. Before the load is applied the atoms are in their equilibrium positions.
  2. Under the applied load the atomic bonds are stretched, but none are broken. The deformation is elastic.
  3. Upon relaxation of the load no bonds are broken, the atoms return to their original equilibrium positions. Elongation is recovered.

Mechanism of springback in plastic deformation:

  1. Before the load is applied the atoms are in their equilibrium positions.
  2. Under the applied load the atomic bonds are stretched and some are rearranged by slip. The deformation has gone past the elastic limit and is plastic.
  3. When the load is released the atoms stay in their new arrangement, however, a certain amount of elastic springback occurs as atoms revert to their equilibrium spacing. Some (but not all) of the elongation is therefore recovered.

This relaxation of the bonds into the equilibrium positions even after plastic deformation is called springback.

Allowance for springback is essential in metal forming processes.

Extra deformation in forming is required to allow for the springback that will occur as a result of the elastic component of the deformation that will be recovered.