Determination of residual resource of flat wagons load-bearing structures with a 25-year service life

The article determines the residual resource of flat wagons load-bearing structures with a 25-year service life. For this purpose, field studies of the technical condition of the load-bearing structures of flat wagons based on the wagon depot of the Foundation of the Southern Railway branch of JSC “Ukrzaliznytsia” were carried out. The flat wagon of model 13-401 was chosen as the subject. It is established that the design service life of the load-bearing structures of the studied flat wagons, taking into account the extension of their operation is not less than 18 years. The strength of the load-bearing structure of the flat wagon in the environment of SolidWorks Simulation (CosmosWorks) software by the finite element method is calculated. It is established that the maximum equivalent stresses occur in the zone of interaction of the spine beam with the pivot be equal to 337.5 MPa. Therefore, the strength of the load-bearing structure of the flat wagons is provided. The estimation of the course of the flat wagons is determined. The research was carried out in the vertical plane during the movement of the butt rail track. The calculation was performed in the MathCad software environment by the Runge-Kutta method. The assessment of the wagon is “excellent”. The conducted researches will promote increase of efficiency of combined transportations in the international communication and strengthening of foreign economic positions of Ukraine in the market of transport services.


Introduction
Ukraine has long been a crossroads of strategically important international transport corridors. Today, the link provides transport logistics between Europe and Asia.
In order to increase the volume of traffic through the territory of Ukraine, combined transport systems have been developed. One of the most promising among such systems are container and piggyback.
It is known that one of the most popular types of wagons in the international combined service are flat wagons. To increase the efficiency of the use of flat wagons in international traffic, their modernization is carried out, which consists in the installation of stationary or folding fitting stops on the load-bearing structure. This allows adapting the load-bearing structures of universal flat wagons to combined transport, in particular container. IOP Publishing doi:10.1088/1757-899X/1021/1/012005 2 At the same time, the level of replenishment of the wagon fleet of Ukraine in recent years is quite insignificant. In this regard, it is possible to determine the residual life of the operated flat wagons, consider the possibility of extending their service life in order to be able to be involved in international traffic. This will ensure the efficiency of combined transportation in international traffic and strengthen Ukraine's foreign economic position in the transport services market.
The substantiation of the extension of the useful life of wagons for the transportation of pellets is covered in [1]. To assess the possibility of further operation of wagons, an experimental determination of the level of load and stress state of the load-bearing structures of wagon bodies based on static, impact and strength tests.
Prediction of the residual life of the hopper dispenser wagon after long operation, taking into account the actual physical and mechanical characteristics of the material of the load-bearing structures is carried out in [2]. A procedure for forecasting the residual life of the load-bearing structure of the wagon has been developed. The results of virtual and experimental studies of the strength of the load-bearing structure of the wagon are presented. However, these studies were performed on hopper wagons. The authors did not study the issue of extending the service life of flat wagons.
The need to adjust the Regulations on extending the service life of freight wagons plying in international traffic is considered in [3]. The expediency of introducing requirements for rolling stock, the service life of which is extended, is substantiated.
Substantiation of options for extending the service life of specialized flat wagons is covered in [4]. Methods of comparative assessment of options for extending the service life of flat wagons, which take into account the economic component of these types of work. Research has been conducted on universal flat wagons, as well as double-decker flat wagons for wagon transportation. Studies on the extension of the service life of flat wagons for the transportation of containers have not been considered in the work.
The study of the possibility of extending the service life of the bodies of universal gondola wagons, which have exhausted their regulatory life, is carried out in [5]. The specified dynamic loadings acting on a bearing design of a gondola wagon taking into account real wear of its elements are defined. However, the authors did not pay attention to the study of the possibility of extending the service life of flat wagons.
Substantiation of measures to extend the service life of freight wagons was carried out in [6]. The scheme of technical diagnostics of freight wagons is developed. It is concluded that it is possible to extend the service life of freight wagons only through the implementation of high-quality technical diagnostics. However, there is no applied use of the proposed measures.
The purpose of the article is to determine the residual life of load-bearing structures of flat wagons with a 25-year service life to justify further use in the international combined service. To achieve this goal, the following tasks are set:  investigate the technical condition of the main load-bearing elements of the frames of flat wagons with a 25-year service life;  to calculate the design service life of the load-bearing structure of the flat wagon;  calculate the strength of the load-bearing structure of the flat wagon;  assess the progress of the flat wagon.

Presentation of the main material of the article
In order to verify the possibility of extending the service life of the load-bearing structure of the flat wagon, the method described in As is known, the backbone and the main longitudinal beams of the flat wagon 13-401 consist of two I-beams №60, which has a variable length. In cantilever parts of a frame height of an I-beam makes 360 mm. To justify the extension of the service life of the flat wagon, field studies of the technical condition of the main load-bearing elements of the frame were carried out based on the wagon depot. The value measured during field studies is the thickness of the I-beam rack ( Figure 2).
where t is determined from the ratio F(t) = γ/2; F(t) is Laplace function, tabular value; σ is standard deviation of the random variable under study, which must be known a priori, even before the experimental measurements; δ 2 is absolute error of measurement result. In technical measurements, the value of measurement reliability is usually taken equal to р = 0.95. When the number of measurements is n = 20, we take the Student's distribution parameter tγ equal to 2.1 Based on the calculations it is established that for the samples given in tables 1 and 2 the number of measurements is sufficient to obtain an adequate assessment of the result.
The used technique in comparison with an expert assessment essentially increases reliability of the chosen decision on appointment of new service life of the wagon. In addition, this technique allows you to determine the residual service life with the same reliability for any number of wagons.
In accordance with the method, the probability of failure Pі elements of the load-bearing structure of the flat wagon in operation is determined by the formula where k is the number of studied wagons; RH is the number of defective elements of one type in the wagon; R is the total number of elements of one type. -the number of faulty structural elements of the wagon of the same name under study is equal to 1 (spine beam) and 2 (longitudinal beam); -indicator of the degree of fatigue curve m = 2; -the strength limit of the load-bearing structure is equal to 490 MPa for steel 09G2D.
The obtained results allowed to conclude that the design service life of the ridge and longitudinal beams of the studied flat wagons, taking into account the extension of their operation is not less than 18 years.
At the next stage, the main indicators of the strength of the load-bearing structure of the flat wagon with the highest amount of wear recorded during field research (Tables 1, 2) were determined. It is established that the mass of the load-bearing structure of the flat wagon, taking into account the wear of its elements, is 3.5% less than the load-bearing structure of the flat wagon, which has nominal dimensions. The strength calculation was performed by the finite element method, which is implemented in the SolidWorks Simulation (CosmosWorks) software environment [9 -13]. The finite element model of the load-bearing structure of the flat wagon is shown in Figure 3. When determining the number of grid elements, the graph analytical method was used [14 -17]. Ten-node isoperimetric tetrahedral were used as finite elements. The number of grid elements was 838084, nodes -274584. The maximum size of the element was 100 mm, the minimum -20 mm, the maximum aspect ratio -4702.9, the percentage of elements with a side ratio less than 3 -39.3, more than 10 -10.2 . The model was fixed in the areas of support of the load-bearing structure on the bogies.  When compiling the design scheme of the load-bearing structure of the flat wagon (Figure 4), the following loads were taken into account: vertical Рv and longitudinal N. It is taken into account that the full load capacity of the flat wagon loaded with conditional cargo is used. The calculation was performed for I and III calculation modes.
The results of the calculation of the strength of the load-bearing structure of the flat wagon in the I design mode "impact" are shown in Figures 5, 6.  The results of the calculation of the strength of the load-bearing structure of the flat wagon at I and III calculation modes are given in Table 3. Based on the calculations, we can conclude that the maximum equivalent stresses occur in the area of interaction of the spine beam with the pivot is not equal to 337.5 MPa. The maximum displacements in the nodes of the load-bearing structure of the flat wagon are recorded in the middle part of the frame -8.6 mm. Therefore, the strength of the load-bearing structure of the flat wagon is provided [18 -20]. In order to use the flat wagon for container transportation, it is possible to install fitting stops on its load-bearing structure.
To determine the assessment of the flat wagon, mathematical modeling of the dynamic load of its load-bearing structure was performed. For this purpose, the mathematical model given in [21] was used. The model takes into account the movement of the wagon in the vertical plane when moving the butt rail track. The calculation is performed for the case of empty wagon movement in the MathCad software environment. The Runge-Kutta method was used as a calculation. Based on the calculations, the accelerations that act on the load-bearing structure of the wagon in the center of mass (Figure 7), in the areas of support on the running gear (Figure 8).   Figure 7 shows that the acceleration of the load-bearing structure of the flat wagon in the center of mass is 5 m/s 2 (0.5g). The acceleration of the load-bearing structure of the flat wagon in the areas of support on the carts is about 7.5 m/s 2 (0.75g), (Figure 8). The acceleration of the carts is about 10 m/s 2 (1.0 g). The obtained results allow us to conclude that the assessment of the wagon is "excellent".

Conclusions
1. The technical condition of the main bearing elements of frames of flat wagons with 25-year service life is investigated. At the same time, field research was conducted based on the wagon depot of the Basis of the Southern Railway branch of JSC Ukrzaliznytsia. The thickness of the leg of the dorsal ridge and the main longitudinal beams of the frame is taken into account as the studied value.
2. The design service life of the load-bearing structure of the flat wagon is calculated. The obtained results allowed to conclude that the design service life of the ridge and longitudinal beams of the studied flat wagons, taking into account the continuation of their operation is not less than 18 years.
3. The calculation of the strength of the load-bearing structure of the flat wagon. The finite element method, which is implemented in the CosmosWorks software environment, is used as a calculation. It is established that the maximum equivalent stresses occur in the zone of interaction of the spine beam with the pivot be equal to 337.5 MPa. The maximum displacements in the nodes of the load-bearing structure of the flat wagon are recorded in the middle part of the frame -8.6 mm. That is, the strength of the load-bearing structure of the flat wagon is provided.
4. An assessment of the progress of the flat wagon. The research was carried out in the vertical plane during the movement of the butt rail track. The acceleration of the load-bearing structure of the flat wagon in the center of mass was 5 m/s 2 (0.5g). The acceleration of the load-bearing structure of the flat wagon in the areas of support on the carts is about 7.5 m/s 2 (0.75g). The acceleration of the carts is about 10 m/s 2 (1.0 g). Therefore, the assessment of the wagon is "excellent".
The conducted research will help to increase the efficiency of the use of flat wagon, and hence the transportation process in international traffic.