5. Improving the fatigue life of a bolt

If we exclude the manufacturing process analyzed above and restrict ourselves to the ISO coarse thread bolt (RT) (using a fine thread for the usual mechanical engineering diameters is never a good solution), we can see that improving the fatigue life of a bolt consists in reducing the stress concentration and gradient at the first thread in engagement. Essentially, this means better distribution of stress between the bolt and nut.

We can :

• reduce clearance (figure 22 );

• use a hanging nut (figure 23 );

• ...