What is a normal bolt
◎Clamping force of bolt
The bolt rotates the nut and tightens the member with the bolt head and nut. It is the same as putting the paper with the rubber band). Tightening force is to destroy the life of at least not destruction, at least until it is necessary. Imagine. When the door is pulled by a strong spring, it is a matter of degree, but the wind does not say that the door is "baton baton". If this baton baton is repeated for many years, I think that it is easy to imagine that somewhere breaks. Even if the wind blows, the door will not break forever. This is why we add a preload.
If two boards are tightened: if the fastening force is insufficient, the two plates are repeated repeatedly, and the plate will be worn or damaged, or scratched some place. In the state where an external force is applied, and the gap occurs in the plate, it goes to destruction as early as the door. When the tightening force is large, there is a considerable difference in the external force below the clamping force.
When the bolt is tightened, the member is recessed and the bolt is in an extended state. In this state, we are in balance.
Loosening the bolt will cause the part to return to its original thickness.
The following is an example of a stress-strain curve that changes when a tensile load is applied to a bolt.
The weight applied to the bolt is preferably designed to the proportional limit (force resistance).
In the case of strength 4.6 class, 400 N / mm 2 strength, 60% of the proof stress → 240 N / mm 2: load is preferred to use below this proof strength
In the case of strength 10.9, 1,040 N / mm2 strength, 90% 940 940 N / mm2 of proof stress: Load is preferred to use below this proof stress