## 3 Results  
Considering the determined parameters of the frame profile, its spatial model was built, and its strength was calculated. When calculating the strength, the finite element method was used, which was implemented in SolidWorks Simulation 2018. When creating the model, the welds between the individual components of the frame were not considered. The finite element model of the frame was formed by tetrahedra elements, and it is depicted in Figure 8, since the finite element mesh was created on a solid body [46; 47; 48; 49; 50]. The number of tetrahedra that formed the mesh was calculated graphically. Taking this into account, the number of nodes was 40,688, and the number of elements was 110,331. The largest element had a size of 100 mm, and the smallest element had a size of 20 mm. The calculation was implemented for two load schemes of the removable module:  
* An action of the vertical load \(P_{V}\) (Figure 9);
* An action of the vertical \(P_{V}\) and longitudinal loads \(P_{L}\) (Figure 10). Figure 8: A finite element model of the removable module. Figure 7: A graph of a definition of optimal structure parameters \(t_{1}\) and \(t_{2}\). \(ABCD\) is an area of acceptable decisions, E is the point of the optimal solution. It was established that the maximum stresses in the removable module structure occur in the zones of interaction of the transverse beams with the longitudinal ones (Figure 11). The maximum stress that arose in these zones was 112.5 MPa (Figure 12), which is lower than the permissible ones for steel grade 09G2S, which are 310.5 MPa. Figure 11: The most loaded zones (marked by the blue) of the removable module when it perceives the vertical load. Figure 9: A scheme of the removable module when it perceives the vertical load \(P_{V}\). Maximum displacements occur in the upper parts of the module structure, and they are about 1 mm (Figure 13). For the case of perception of the vertical and longitudinal loads by the removable module, the most loaded zones are the zones of interaction of transverse beams with longitudinal ones, which are located on the side of the loaded fittings (Figure 14). Figure 14: The most loaded areas (marked by the blue) of the removable module when it perceives the vertical and longitudinal loads. Figure 12: The distribution of stresses in the removable module when it perceives the vertical load. Figure 13: Displacements in the nodes of the removable module when it perceives the vertical load. The maximum stress that arose in these zones was 287.6 MPa (Figure 15). These values are lower by 7.4% than the permissible ones. The maximum displacements of the removable module structure occur in the end wall located on the side, where the load acts on it (Figure 16). These displacements amounted to a value of 2.16 mm. Bench tests were conducted in the research laboratory of the \"Center for Diagnostics of Transport Structures\" at the Ukrainian State University of Railway Transport (Kharkiv) in order to experimentally substantiate the use of the removable module. This study was conducted on an example of the unloading hatch cover of an open wagon, which is a component of its floor. The determination of the stresses that arise in the hatch cover structure was carried out using the method of measurement by means of the electrical strain gauges. The installation  
Figure 16: Displacements in the nodes of the removable module structure when it perceives the vertical and longitudinal loads. Figure 15: The distribution of stresses in the removable module structure when it perceives the vertical and longitudinal loads. of strain gauges was carried out according to a gauge scheme. The locations of the strain gauges on the hatch cover were determined based on the theoretically obtained stress fields that arise in the hatch cover, and they are shown in Figure 17.  
The strain gauges were calibrated (Figure 18) before their installation in the hatch cover structure. Strain gauges with a base of 10 mm and a resistance of 100 Ohms were used.