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Bolt connection is a common fastening connection in mechanical design and engineering problems. Generally, in the strength design and verification of connecting bolts, the bolt preload is calculated according to the external load on the bolt, and then the strength is calculated according to the calculation formula under different working conditions, such as the analysis and calculation of static load and dynamic load. Therefore, the finite element analysis method obtains the bolt external load through the overall assembly model of bolt connection, and then designs the bolt through manual calculation.

However, the behavior of bolted connections is quite complex. For typical bolted connections, subject to the influence of various factors, the combination of parameters that must be considered from the initial pre tightening to the final bolt change load is quite confusing, especially considering the failure of bolted connections. Therefore, it is more important to accurately construct the characteristics of bolted connections.

Based on different bolt connection design requirements, the analysis model is treated differently in finite element analysis. Several methods of bolt connection modeling in the analysis model are given below:

1. bolts do not participate in modeling, and the connection between parts uses binding contact, without bolt preload; This kind of bolt free and binding contact is the simplest method for the modeling of bolted connection components. The simplified method can define binding contact on the contact surface of the connecting components, which is the fastest to solve. However, this simplified method will make the structure too rigid because of binding the connecting surface of the whole component, and the load of each bolt cannot be obtained. If you need to obtain the bolt reaction, you can also use more detailed analysis, that is, define binding contact for the contact surface within the action range of each gasket diameter, so that the bolt reaction can be obtained on the independent contact surface, but the torque can not be obtained directly (APDL command is required).

1. create beam connections directly in the model. Instead of creating a beam model, you can directly create a beam connection by directly defining the beam element to the edge or face of the part. A beam element is used for mesh generation. The cross section must be a circular section, and the bolt preload cannot be directly applied (APDL command needs to be supplemented). It is more practical for the beam element to be connected to the action surface corresponding to the gasket diameter. The force transmitted by the beam element is distributed on the gasket surface, and the force and torque on the beam element can be obtained for subsequent manual calculation of the bolt range. This connection method is commonly used in the aerospace industry. The bolt bears all the loads, which is usually more conservative. Subsequent calculations determine whether the bolt is invalid.

1. use the line body in the model. Create a line body in DM, define the cross-section parameters of the beam, and import structural analysis. The line body usually uses fixed joints to connect the beam element to the edge or face of the part. The line body can be divided into multiple beam elements. Any cross-section is specified in DM, and the bolt preload can be directly applied. This method is commonly used in the verification of pressure vessel pipe flanges.

1. the bolt is a solid model without thread, and the pre tightening force is considered; If more detailed features of bolted connection are considered, such as contact behavior between parts, bolts, gaskets and nuts, solid element modeling can be used. The simple processing method can adopt binding contact, and the complex processing method adopts friction modeling. Considering the calculation cost, the actual modeling does not include threads.

1. the bolt is a solid model with threads, and the pre tightening force is considered; The geometric correction of bolt thread contact is one of the new functions of WB. This feature treats the bolt concentrated force as the distributed force on the bolt connection surface, which is closer to the real state of bolt stress distribution.

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