Used in high-strength nut pair, the strength grade (after heat treatment) is grade 10, used 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 is to bear the external load by applying the pretension P inside the nut, and then generating the friction resistance on the contact surface between the connected parts, while the ordinary bolt bears the external load directly.
The strength nut connection has the advantages of simple structure, good mechanical properties, detachable, anti fatigue, no loosening under dynamic load and so on. High strength nuts are tightened with special spanner to produce huge controllable preload. Through the nut and the backing plate, the same preload is generated on the connector. Under the action of preload, there will be a lot of friction along the surface of the connector. Obviously, as long as the axial force is less than this friction, the component will not slide and the connection will not be damaged. This is the principle of high strength nut connection.
High strength nut connections prevent sliding by friction between contact surfaces. In order to make the contact surface have enough friction, it is necessary to increase the clamping force and the friction coefficient of the contact surface. The clamping force between members is realized by pre tension on bolts, so bolts must be made of high strength steel, which is also called high strength bolt connection.
In high strength bolted connections, the friction coefficient has a great influence on the bearing capacity. The results show that the friction coefficient is mainly affected by the form of contact surface and the material of parts. In order to increase the friction coefficient of the contact surface, sandblasting and wire brush cleaning are often used to clean 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 caused by design load does not exceed the friction force.
The design standard of high strength bolts under pressure is not to cut off the shaft or crush the plate. In addition, high strength bolts cannot be reused.
