Yield strength concept
The yield strength is the yield limit when the metal material yields, that is, the stress that resists the slight plastic deformation. For metal materials that do not exhibit significant yielding, the stress value that produces 0.2% residual deformation is specified as the yield limit, called the conditional yield limit or the yield strength.
An external force greater than the yield strength will permanently invalidate the part and will not recover. For example, the yield limit of low carbon steel is 207 MPa. When the external force is greater than this limit, the parts will be permanently deformed. If it is smaller than this, the parts will return to their original appearance.