# 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
Therefore, the following simulation sequence was set in this paper: single-bolt sequence tightening: 1\(\rightarrow\)2\(\rightarrow\)3\(\rightarrow\)4\(\rightarrow\)5\(\rightarrow\)6\(\rightarrow\)7\(\rightarrow\)8; single-bolt interval tightening: 1\(\rightarrow\)3\(\rightarrow\)5\(\rightarrow\)7\(\rightarrow\)2\(\rightarrow\)4\(\rightarrow\)6\(\rightarrow\)8; single bolt interval two-bolt tightening: 1\(\rightarrow\)4\(\rightarrow\)7\(\rightarrow\)2\(\rightarrow\)5\(\rightarrow\)8\(\rightarrow\)3\(\rightarrow\)6; single-bolt diagonal tightening: 1\(\rightarrow\)5\(\rightarrow\)2\(\rightarrow\)6\(\rightarrow\)3\(\rightarrow\)7\(\rightarrow\)4\(\rightarrow\)8. The preload was set to 72 KN and the time step was used to control the bolt tightening sequence. In order to ensure the accuracy of the simulation results without mutation, a total of 96 steps were set. With 96 load steps, every 8 load steps, the bolt stress value reached  
Figure 5: Finite element mesh generation of the aviation component. 72 KN. At step 96, the preload of all bolts was 72 KN. The maximum gap between the aviation component front section cabin and the control cabin was 0.1 mm, and the axis inclination angle was 0.2\({}^{\circ}\). The maximum deformation curve of the aviation component is shown in Figure 6.  
It can be seen from Figure 6 that the maximum deformation of the aviation component corresponding to sequence tightening and interval tightening exceeded 1 mm. Among the four tightening sequences, the deformation of the aviation component caused by sequence tightening was the largest. The deformation of the aviation component caused by interval two-bolt tightening was close to 1 mm, and the deformation caused by diagonal tightening was the smallest, at about 0.8 mm. Using the above four methods to tighten the aviation component, the maximum deformation reached the peak value many times, and the damage was serious. In addition to observing the maximum deformation of the aviation component, the magnitude and uniformity of the residual preload of bolts were also taken as evaluation parameters. We compared the tightening sequences as good or bad based on these two characteristics. In addition to using finite element simulation to measure the bolts' residual preload, an ultrasonic measuring instrument was used to measure the residual preload of the bolts. The name of the measuring equipment was an electromagnetic ultrasonic double-wave bolt stress instrument, and the equipment model is ST100, as shown in Figure 7. As the temperature affects the speed of the ultrasound, the experiment temperature remained unchanged. The accuracy of the instrument is less than \(\pm\)3%, which ensured the precision of the experiment. An ultrasonic generator was installed at the bolt end, to measure the time delta between the transmitting and receiving signals of the ultrasonic equipment under the conditions of unscrewed and screwed bolts. The deformation of the bolt during the tightening process was calculated. By multiplying the deformation by the cross-sectional area of the bolt, the elastic modulus of the bolt material, and then dividing by the clamping length of the bolt, the preload of the bolt could be obtained. The residual preload of the bolts in the above four sequences was measured with an ultrasonic measuring instrument and compared with the simulation value under the condition of a 0.1 mm gap. The results are shown in Figure 8.  
Figure 6: Maximum deformation diagram of 0.1 mm gap value aviation component with single bolt. It can be seen from Figure 8 that the maximum error between the simulation value and the experimental value of the four sequences was less than 45.0, which accounted for 0.75% of the simulation value. This verified the correctness of the simulation results. The average values of the four tightening methods' residual preload were 59,946 N, 60,915.1 N, 60,847.9 N, and 60,775.5 N, respectively.