The stresses in extra full-length leaves are 50% more than the stresses in graduated-length leaves.
One of the methods of equalising the stresses in different leaves is to pre-stress the spring.
The pre-stressing is achieved by bending the leaves to different radii of curvature, before they are assembled with the centre clip.
As shown in Fig, the full-length leaf is given a greater radius of curvature than the adjacent leaf.
The radius of curvature decreases with shorter leaves. The initial gap C between the extra full-length leaf and the graduated-length leaf before the assembly, is called a ‘nip’. Such pre-stressing, achieved by a difference in radii of curvature, is known as ‘nipping’.