## 3 Results  
Taking into account the selected profiles of the detachable module frame, its spatial model was created, and the strength calculation was performed in SolidWorks Simulation [38; 39; 40]. The finite element model (Figure 14) was formed by a spatial tetrahedral [40; 41]. This element type was chosen due to the fact that the mesh was formed on a solid body. The optimal number of grid elements is determined by the graphoanalytical method. The method is based on a graphical (geometric) representation of admissible solutions and the objective function of the problem. The essence of the method for solving this problem is to construct the dependence of the maximum equivalent stresses on the number of finite elements. When this dependence begins to be described by a horizontal line, this is the optimum number of finite elements. Taking this into account, the model has 150,474 elements with a maximum size of 100 mm and a minimum size of 20 mm, as well as 55,221 nodes. When creating the mesh, it is automatically compacted in the areas of rounding and conjugating individual elements. The design diagrams of the detachable module are shown in Figure 15. In these diagrams, the designation of the forces is identical to those shown in Figures 4 and 9, respectively. Connections are applied to the fitting stops of the detachable module to simulate its interaction with the fitting stops of the flat car. The construction material of the detachable module is low-alloy steel 09G2S. This steel grade is one of the most commonly used in the car building industry for the construction of vehicles [25]. When conducting calculations,  
Figure 14: Finite element model of the detachable module. Figure 13: Structural channel overlapped with a vertical sheet. welding seams between individual components of the removable module were not taken into account, i.e., the design was considered monolithic. The results of the calculation of the detachable module are shown in Figures 16 and 17. Analyzing the results, it can be concluded that the maximum stresses in the structure of the detachable module at mode I occur in the cross bearers in the areas of their interaction with the fittings; they amount to 286.5 MPa (Figure 16a). The resulting stresses are lower than permissible by 7.7%. The stresses equal to 310.5 MPa are taken as permissible [25]. These stresses are accepted as permissible, since at mode I, the permissible stresses in accordance with the regulatory document [25] are taken as equal to 0.9\(\sigma_{y}\), where \(\sigma_{y}\) is the yield strength of the material. For steel grade 09G2S, it is 345 MPa. The maximum displacements in the detachable module structure at mode I occur in the upper belt of the end superstructure and amount to 4.1 mm (Figure 17a). This distribution of displacement fields is explained by the fact that the superstructure interacts with the detachable module components on all sides, and its upper part is free. At mode II, the maximum displacements are recorded in the central posts on the tilt side of the detachable module. These displacements are 6.2 mm (Figure 17b). Their presence can be explained by the fact that the vertical post is fixed at the bottom while its upper end is free. Figure 16: Stress state of the detachable module: (**a**) mode I; (**b**) mode II. Figure 15: Design diagrams of the detachable module: (**a**) mode I; (**b**) mode II. At mode II, the maximum stresses are recorded in the main longitudinal beam on the tilt side of the detachable module and amount to 292.4 MPa (Figure 16b). These stresses are concentrated in the areas of interaction between the main longitudinal beam and the fitting stops. However, they do not exceed the permissible ones and are 5.8% lower. It should be noted that the obtained displacement fields are consistent with the diagrams shown in Figures 8 and 11. To ensure safe operation of the detachable module, its modal analysis was carried out. This was performed using the built-in options in SolidWorks Simulation (version 2015).