Mechanical properties of common bolts and high strength nuts

For high strength nuts and bolts, the strength grade (after heat treatment) is grade 10, which is used together with grade 10.9 bolts.
The mechanical properties and calculation methods of ordinary bolts and high strength nuts are different. The force of high-strength nut first applies pre tightening force P in its interior, and then produces friction resistance on the contact surface between the connectors to bear external load, while ordinary bolt directly bears external load.
The high strength nut connection has the advantages of simple structure, good mechanical performance, replaceable, anti fatigue and no loosening under dynamic load. This is a promising connection method.
High strength nut is to use a special wrench to tighten the nut, which makes the bolt produce huge and controllable pre tightening force. The same amount of preload is produced on the connecting parts by means of nuts and backing plates. Under the action of preload, the friction force on the surface of the connector will be larger. Obviously, as long as the axial force is less than this friction force, the member will not slide and the connection will not be damaged. This is the principle of high strength nut connection.

High strength nut connections are prevented by friction between the contact surfaces of the connector. In order to make the contact surface have enough friction force, it is necessary to increase the clamping force and the friction coefficient of the contact surface. The clamping force between components is realized by applying pre tightening force to bolts, so bolts must be made of high strength steel, which is why it is called high strength bolt connection.
In the high strength bolt connection, the friction coefficient has a great influence on its bearing capacity. The results show that the friction coefficient is mainly affected by the contact surface shape and the component material. In order to improve the friction coefficient of the contact surface, sandblasting and wire brush cleaning are usually used to treat the contact surface of the parts within the connection range.
In fact, there are two types of high strength nuts: friction type and pressure type.
The shear force criterion of friction type high strength bolt is that the shear force generated by design load does not exceed the friction force.
The bearing type high strength bolt is designed according to the principle that the rod body is not damaged or the plate is not crushed.
In addition, high strength bolts cannot be reused.
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