Three turns of the screw takes half a turn. Do you know why?

Recently, I was watching someone’s speech, saying that Germans are rigorous in doing things. They said that when screwing a bolt requires three turns and a half turn, the Chinese just twist two and a half turns.

I don’t understand why I don’t need a torque wrench. Why do I need to retract a half-turn, and where will I tighten it and then push a half-turn? Are you afraid of the bolts loosening? Or is it the speaker's own compilation?

These three circles are 360°*3, and the half circle is 180°? Or this degree may be only 15 degrees. How the workers control this half circle, and the reason why the Germans twist the screw three times and then half a circle when screwing the screw, there is actually a scientific basis.

When the screw is tightened, in order to prevent loosening, an additional pre-tightening force should be applied, and the pre-tightening force will be eliminated after half a turn of loosening. The screw is in elastic deformation after tightening, especially under the condition of high temperature and vibration load. Such continuous pressure will cause creep for a long time. After the screw becomes plastic deformation, its strength will drop significantly or even fail.

The retraction of a half circle is to restore the elastic deformation and eliminate the pre-tightening stress, so that regardless of the continuous pressure deformation of the screw or the elastic deformation, the probability of plastic strain and failure is greatly reduced, so that the screw can maintain a continuous high strength Pressure, and direct tightening can not achieve such an effect.

It is precisely because of this that in most German high-end machinery and equipment factories, when assembling special parts, tightening screws is guided by strict operation manuals, and there are clear specifications for how much torque is applied.