The required longitudinal elongation is theoretically determined by the elastic resilience of the bolt.



Symbols used

AN	Nominal bolt cross section	mm²
A3	Thread core cross section	mm²
AS	Bolt thread tension cross section	mm²
ES	Young's modulus of the bolt	205.000 N/mm²
FM	Mounting tension force	N
F0.2	Bolt force at minimum yield point	N
l1	Elastic bolt length	mm
l2	Elastic thread length	mm
Δl	Linear deformation at bolt tightening	mm
δS	Elastic resilience of the bolt	mm/N
Rp 0.2	Tension at yield point of bolt material	N/mm²
lk	Clamping length of the bolt	mm
lGM	Thread length lG and nut displacement lM · lGM = lG + lM used in calculating the resilience of the inserted thread portion.	mm

This gives:





with l_G = 0.5 · d and l_M = 0.4 · d

for nuts ac. to DIN 934



The force allocated to the elastic longitudinal elongation is:



Calculation module