Mechanical properties of ordinary bolts and high-strength nuts

Mechanical properties of ordinary bolts and high-strength nuts

Used for high-strength nuts and bolts, with a strength grade (after heat treatment) of 10, and used in conjunction with grade 10.9 bolts.

The mechanical properties and calculation methods of ordinary bolts and high-strength nuts are different. The force on high-strength nuts first applies a pre tightening force P internally, and then generates frictional resistance on the contact surface between the connectors to withstand external loads, while ordinary bolts directly bear external loads.

High strength nut connections have the advantages of simple structure, good mechanical performance, replaceability, fatigue resistance, and non loosening under dynamic loads. This is a promising connection method.

High strength nuts are tightened with a special wrench to produce a huge and controllable pre tightening force on the bolt. Generate the same amount of preload on the connecting components through nuts and pads. Under the action of preload, the surface of the connecting piece will generate significant friction. Obviously, as long as the axial force is less than this frictional force, the component will not slide and the connection will not be damaged. This is the principle of high-strength nut connection.

The high-strength nut connection is prevented by friction between the contact surfaces of the connector. In order to provide sufficient friction on the contact surface, it is necessary to increase the clamping force of the component and the friction coefficient of the contact surface. The clamping force between components is achieved by applying pre tightening force to the bolts, so the bolts must be made of high-strength steel, which is why they are called high-strength bolt connections.

In high-strength bolted connections, the friction coefficient has a significant impact on their bearing capacity. The results indicate that the friction coefficient is mainly influenced by the shape of the contact surface and the material of the component. In order to improve the friction coefficient of the contact surface, sandblasting and wire brushing cleaning methods are usually used to treat the contact surfaces of components within the connection range.

In fact, there are two types of high-strength nuts: friction type and pressure type.

The shear force criterion for friction type high-strength bolts is that the shear force generated by the design load does not exceed the frictional force.

Bearing type high-strength bolts are designed based on the principle that the rod body is not damaged or the plate is not crushed.

In addition, high-strength bolts cannot be reused.