# Mechanical Stress Prediction of an Aircraft Torque Tube Based on the Neural Network Application
## 6 Brake-Assembly Finite Element Analysis  
The brake assembly was meshed in the ANSYS software using HEXA elements, which were of high quality; the HEXA elements were also used to reduce the number of elements in the finite element model (FEM) [51]. The FEM model is shown on the left side of Figure 6. It can be clearly seen that the mesh is finer in the area of interest, which is the torque tube. The right side of Figure 6 represents the application of the boundary condition; the temperature is shown in red, and the centrifugal force applied and is represented by the yellow arrow. The assembly was fixed in the holes shown in purple in Figure 6. The boundary conditions are represented by the speed of the aircraft, from which the centrifugal force was calculated, followed by the temperature of the brake during landing. The third parameter that affected the stress was the ambient temperature. The contacts with the corresponding friction coefficient are defined between the individual parts [52]. The material properties of the parts were applied as described in the previous sections. A static structural analysis was performed for 36 regimes, which were defined by the aforementioned parameters. For example, three of the thirty-six regimes are mentioned in Table 2. The regimes represented some of the states of the brake during the aircraft operation and simulated real conditions [51; 52].  
Figure 5: Three-dimensional model of a brake assembly of the Airbus A320 modeled in ANSYS software.  
Figure 6: Finite element model and application of the boundary condition.  
A pressure of 14.47 MPa was applied on the surface of the first plate in order to simulate the action of the braking valves and squeezing plates. The FEM model consists of 204,469 elements and the elapsed time of the static structural analysis was 1716 s. The results of the study are represented by the stress calculated for the 36 regimes of the brake operation; one of these regimes is shown in Figure 7. The boundary conditions stand for the temperature of the brake during the operation, which was at 260 \({}^{\circ}\)C, the outside temperature of 40 \({}^{\circ}\)C, and the aircraft's landing speed of 300 km/h.  
The temperature had the most significant impact on the torque tube, which was caused by the friction between the stator and rotor plates during the landing of the aircraft until the aircraft stopped. The maximal Von Misses stress of the brake was 699.98 MPa, and it was concentrated in the torque tube in the area of the ribs. A detailed view is shown in Figure 8.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Regime** & **Brake Temperature \({}^{\circ}\)C** & **Outside Temperature \({}^{\circ}\)C** & **Landing** & **Stress MPa** \\ \hline
1 & 200 & 25 & 200 & 472.36 \\ \hline
2 & 240 & 25 & 220 & 533.42 \\ \hline
3 & 260 & 40 & 260 & 645.98 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Inputs for the neural network.  
Figure 8: Von Misses stress distribution in the torque tube of the brake.  
Figure 7: Von Misses stress of the brake assembly.  
Analogically, the FEM analysis was performed for 36 operational regimes and 36 mechanical stresses were calculated. The estimated Von Misses stresses were used as target inputs for the NN-training process.