Introduction

Brazil currently has more than 30,000 kilometers of railroads within its borders [1]. These railroads are responsible for transporting people and materials along their entire length. In this regard, from an engineering perspective, railroads and railcar trainsets can be the subject of studies across various disciplines. Consequently, a company wished to conduct a study of one of its rail car bogies and requested that Kot Engenharia an analysis of a rail car bogie cross member. 

The bogie model in question is called “Three-Piece” and consists of two side frames and a center cross-member. Among the main functions of this bogie are guiding the vehicle through curves and distributing the vertical loads from the car body to the wheels. Figure 1 is a photograph of the bogie under analysis.

Figure 1: Photograph of the railroad switch. [2]

Due to cyclic loading on the central crossbeam, cracks often appear in the internal ribs and at the “spindle center.” In this context, the scope of the service provided by Kot aimed to conduct simulations to define criteria for scrapping the bogie crossbeams, as well as to propose structural modifications focused on extending the component’s service life and, consequently, reducing the risk of failure. Read this article to learn more about the company’s work!

Development

First, the project began with the creation of as-built drawings of the cross-section. Subsequently, based on the information collected, a three-dimensional model of the object’s geometry was created. In addition, the 3D model was refined to remove details unnecessary for the analyses, and a mesh was generated for analysis using finite element analysisusing specialized software. Figure 2 illustrates this stage of the process.

Figure 2: Finite element model of the crossbeam. [2]

Prior to Kot’s study, the company installed strain gauges on the cross member andside frame of the car bogie. Data was collected over the course of five trips along the railway route. Thus, based on the data obtained from strain gauges, it was possible to determine the deformations caused by the vertical loads acting at the center of the sleeper.

One of Kot’s staff members visited the company’s workshop to gain a better understanding of the cracks in the crossbeams, learn about the repair process, and document defects in crossbeams that were either being repaired or scrapped.

According to the information gathered during the visit, the main areas where cracks appear are the internal ribs and the center of the spindle, as shown in Figure 3.

Figure 3: Sections of the crossbeam with the highest incidence of cracks. [2]

The computational simulation plan used in the crack propagation analysis is presented in a flowchart showing some of the steps followed in Figure 4.

Figure 4: Flowchart of the sleeper analysis procedure. [2]

Once the analysis assumptions—such as loading conditions, crack types, and propagation scenarios to be evaluated, as well as the boundary conditions of the computational model—had been defined, the simulations were run. Figure 5 shows one of the results obtained during the static analysis of the crossbeam. Figure 6 illustrates the results obtained for some of the crack propagation simulation scenarios considered.

Figure 5: Results of the static analysis of the crossbeam. [2]

Figure 6: Evolution of crack length for some of the scenarios considered as a function of fatigue life. [2]

Finally, after completing all simulations and analyzing the results, it was determined that geometric modifications to the current crossbeams were not feasible due to restricted access to the interior of the crossbeams where the internal ribs are located. Consequently, the proposed modifications pertained to the design of new crossbeams to be purchased by the company. In addition, one of the suggested modifications to the object’s geometry can be seen in Figure 7.

Figure 7: Proposed geometric modifications for new crossbeams. [2]

The simulations were rerun taking into account the proposed changes, and one of the results is shown in Figure 8.

Figure 8: Results of the static analysis of the modified crossbeam. [2]

Conclusion

Elastic Linear Fracture Mechanics (ELFM) is a fatigue life assessment methodology based on the principle that every component inevitably contains imperfections and defects, whether due to the manufacturing process or the operating conditions under which it is used. As such, it represents an advance over traditional fatigue analysis methods, which do not account for the effects of cracks in the material. In fact, these analyses are complex and challenging; however, upon completing a study, it is possible to obtain satisfactory results and, consequently, unique solutions for each analysis case.

Finally, Kot has a team of qualified professionals who can assess a wide range of needs and work with the client to find the best solution to their problem. Contact our team for more information!

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References:

[1] Rail Transport in Brazil, Percília Eliane, [n.p.]. Available at: https://brasilescola.uol.com.br/brasil/transporte-ferroviario-brasileiro.htm

[2] Kot Engenharia Collection.