# Research on Prediction Method of Bolt Tightening for Aviation Components Based on Neural Network
## 3 Aviation Component Bolt Tightening
### Verification of the Tightening Scheme Based on a Finite Element Simulation Method  
As the aviation component cannot be seamlessly docked during the docking process, there will be a gap between the control cabin front section and the aviation component front section cabin, as shown in Figure 4. During the process of aviation component bolt tightening, the gap between the control cabin and the aviation component front section cabin will affect the tightening process. Therefore, in the process of bolt tightening and subsequent analysis, the gap between the control cabin front section and the aviation component front section cabin is considered. As described in Section 2, the gap value is known in the process of building the finite element model and subsequent surrogate model of the aviation component bolt tightening. Figure 4: The gap of the aviation component. A finite element simulation model of the aviation component bolt tightening was constructed with Ansys Workbench. The aviation component material and bolt material were all high strength steel, its Young's modulus was 209 GPa at room temperature, and the Poisson's ratio was 0.29. In order to improve the accuracy of the calculation, the mesh on the contact surface was subdivided. Due to of the irregular shape of the aviation component, the main volume of the aviation component was divided into different volumes to apply the hex dominant meshing method. The mesh cell size was set to 4 mm. The grid of the bolt and the screwed surface was refined, and the grid of the fixed support (bottom surface) was roughened. The grid was generated following the above method, the aviation component generated 683,712 nodes and 341,801 cells, as shown in Figure 5.  
In the connection setting of the finite element simulation model, the contact type between the bolts and the aviation component front section cabin was set as\"non-separation\". The contact type between the screw and the bolt hole was set as\"frictional\" contact, and the contact type between the control cabin front section and the aviation component front section cabin was set as\"frictional\" contact; the friction coefficient was 0.2 (0.2 is the friction coefficient between a rigid body and another rigid body). The Lagrange algorithm was used as the contact formula in advanced settings to improve the calculation accuracy. In order to improve the convergence of calculation, the contact behavior mode was set to symmetrical contact. The small sliding algorithm was used to improve the convergence rate. In the case of considering the gap between the control cabin front section and the aviation component front section cabin, tightening the bolts with a small gap first made the bolt tightening face corresponding to the large gap tilt upward. The result was that there was a bigger gap between the control cabin front section and the aviation component front section cabin. This larger gap and the larger deformation of the aviation component would make the bolt tightening more difficult and produce an uneven residual preload of the bolts. Therefore, the bolts located at the larger gap should be tightened first. The bolt at the largest tightening gap was marked as bolt 1. The number of bolts that needed to be tightened between the control cabin front section and the aviation component front section cabin was only eight, and the eight bolts were symmetrically and evenly distributed. After tightening bolt 1, tightening bolt 8 or bolt 2 would have the same effect.