Introduction

Currently, with a network spanning over 31,000 kilometers across the country, the rail system connects major mining and steel centers, as well as linking industrial and agricultural hubs to Brazil’s main ports. Consequently, due to the significant cargo capacity of locomotives, railways excel at transporting large volumes of products and raw materials, which helps reduce transportation distances and consequently lowers costs for companies and prices of consumer goods.

Given this, the continuous increase in railway use leads to wear and tear on assets, which can compromise the maintenance of their structures and the safety of operations. For example, fatigue can occur in rails and components as a result of increased axle loads and/or changes in the speed of locomotive and railcar trainsets.

In this regard, the use of instrumentation techniques makes it possible to monitor dynamic effects on railcars, locomotives, and track infrastructure. This enables the collection of data for more informed decision-making, which ensures the proper functioning of operations and reduces the costs of corrective maintenance—be sure to review the examples presented in the articles Railway Instrumentation and Succes story: Railway Instrumentation.

In this context, one of our clients requested an analysis of the conditions of a gondola car’s bogie, in light of the increased ore load on the car. An assessment of the forces acting on the bogie was required through strain gauges, as well as monitoring of the suspension spring travel and bearing temperature.

In addition, the study in question made it possible to estimate the service life of the bogie, given the railcar’s operating conditions, through fatigue analysis. The information and conclusions from the work performed by Kot enable the client to conduct a comparative and quantitative analysis of the costs involved in its logistics process, such as preventive maintenance, freight pricing, and other operating costs.

Field instrumentation

First, the railway bogie—consisting of two side members (Figure 1) and a cross member (Figure 2)—was instrumented to continuously collect the required data under actual operating conditions during three train travel cycles. Thirteen strain gauges, one GPS unit, two thermocouples, and two load cells were installed.

To this end, the sensors in question were strategically deployed to assess and monitor, respectively, the stresses acting on the components, the railcar’s geolocation, the temperature of the bearings, and the displacement of the suspension system. Next, all were connected to an onboard data acquisition system, and the data obtained in real time were recorded for subsequent processing and correlation with the wagon’s loading, transfer, and unloading stages. Figures 1 and 2 show the individual models of the bogie’s side and cross member, respectively.

Figure 1: Computer model of the side of the bogie. SOURCE: Kot Collection.

Figure 2: Computer model of the bogie crossbar. SOURCE: Kot Collection.

Development and calibration of the computer model

Next, a finite element model (FEM) of the truck was developed in CAE (Computer Aided Engineering) software, based on a dimensional survey conducted in the field (as built), reproducing the geometry of the asset in detail. The computational model generated can be seen in Figure 3 below.

Figure 3: Computer model of the trick. SOURCE: Kot Collection.

Subsequently, to validate the model, the components were analyzed separately based on the forces recorded by the strain gauges during the loading of the railcar. Figures 4 and 5 show the deformation results obtained during the calibration.

Figure 4: Deformations obtained in the bogie beam during model calibration. SOURCE: Kot Collection.

Figure 5: Deformations obtained on the sides of the bogie when calibrating the model. SOURCE: Kot Collection.

Thus, using the calibrated model, a structural analysis was performed to evaluate the forces acting at the sensor installation points under three different loading conditions. Based on these results, the stress at the rail support was evaluated, and the corresponding equivalent von Mises stresses were determined.

Analysis of the wagon's operating cycle

Next, a static structural analysis was performed based on data obtained from strain gauges attached to the top and inner surface of the bogie during the car’s operational cycle. The first sensor was used to measure deflection caused by the car’s vertical load, and the second to measure deflection caused by lateral load. The deformations recorded by these sensors are shown in Figures 1 and 2.

Graph 1: Strain values on the strain gauge located at the top of the bogie. SOURCE: Kot Collection.

Graph 2: Strain values on the strain gauge located inside the bogie. SOURCE: Kot Collection.

Thus, the peak values were used to quantify the applied forces and, consequently, to determine the stresses in the stress concentration zones. Figure 6 illustrates the results of this analysis, highlighting the rail supports in the computational model.

Figure 6: Voltage concentrators in the computer model. SOURCE: Kot Collection.

Based on this, it was concluded that the variations in lateral load on the truck (Figure 2) have a greater amplitude than those of the vertical load (Figure 1), which increases stress in the stressed regions and reduces the component’s service life due to fatigue.

Analysis of bearing temperatures

However, the onboard system recorded only changes in ambient temperature throughout the three trip cycles. As for the bearing temperatures monitored by the thermocouples, no significant variations were detected; they remained within the bearings’ operating temperature range.

Suspension spring travel analysis

With regard to assessing dynamic displacement, the load cells monitored data on the travel of the suspension springs. Some of the values recorded during the journey with the wagon loaded with ore can be seen in Graph 3 below.

Graph 3: Travel of the suspension springs during the journey of the loaded wagon. SOURCE: Kot collection.

The dynamic analysis showed that the loading in question resulted in a displacement of the suspended mass. In general, spring compressions were observed in the sections where the wagon was loaded and no distensions were identified in the unloaded sections, due to load relief. The frequency of the suspension oscillations is shown in graph 4, with 2 Hz being the main frequency during the three cycles monitored.

Graph 4: Suspension oscillation frequency. SOURCE: Kot collection.

Fatigue analysis

As for the fatigue analysis of the bogie, a useful life of 61 years was estimated for a load of 132.9 tons of ore. For loadings of 133.7 and 134.9 tons, reductions of 28% and 44% respectively were observed in the component's useful life when compared to 61 years. The peaks with the greatest influence on the bogie's useful life are highlighted in Graph 5.

Graph 5: Peaks with the greatest influence on bogie service life. SOURCE: Kot Collection.

By excluding the critical peaks from the analysis, the useful life was recalculated as 69, 55 and 42 years for shipments of 132.9, 133.7 and 134.9 tons of ore, respectively.

Conclusion

It is well known that the wear and tear on wagon components and structures is inherent to rail transport operations, a modality that is growing more and more on the national scene. According to ANTF (National Association of Railway Transporters), in 2021, the rail freight sector grew by 506.8 million useful tons (TU), 3.6% compared to 2020.

With this in mind, the instrumentation aims to monitor and detect the areas of the railroad where the most damage to trains occurs, which compromises the safety and logistics of freight transport.

In this regard, we would highlight the service carried out by Kot, in which the monitoring and evaluation of the dynamic effects on the wagon's components was carried out, making it possible to offer the client greater reliability in making data-based decisions, with a view to reducing future costs.

In view of the above, the excessive variations in compression and load relief of the suspension travel and the influence of ore loading on the useful life of the bogie were the highlights of this study. With regard to the variations recorded on various sections of the railroad, the most pronounced occurred in curves and in the areas of the old permanent way yards.

In addition, the main causes of the component's reduced lifespan are the lateral loads imposed on the bogie during journeys. Once identified, the main causes and the data collected on the stretches become fundamental inputs for the client to draw up studies of ideal loads and speeds for transportation, which will be adopted to mitigate premature wear and derailment risks by means of strategic and specific interventions.

Among other gains, the study of the useful life of the components of the wagons, as well as the permanent way, allowed the client to predict expenses with replacements and interventions, resulting in a more assertive forecast of logistics costs.

It is clear, therefore, that instrumentation techniques are extremely relevant for the management and maintenance of railway asset integrity. In this regard, Kot has a team of qualified professionals to develop the best engineering solutions for the challenges inherent in the day-to-day operations of the railway mode. Consult our team for more information!

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