Introduction

Instrumentation work on railroads is developed to monitor the physical quantities (accelerations, speeds, temperature, etc.) involved in this complex operating process. The instrumentation techniques used make it possible to understand and evaluate the dynamic effects caused on the trains (wagons and locomotives) and the permanent way. Monitoring this data makes it possible to acquire information for decision-making.

According to the National Association of Railway Transporters (ANTF), 493.8 million tons were transported in 2019, an increase of 95% since the concessions began in 1997. Today, more than 95% of minerals reach Brazilian ports by rail. In the case of the modal, more than 45% of everything transported is solid agricultural bulk for export. [1]

In view of the above, the growing, continuous and significant increase in the use of railroads can also cause problems related to the conservation of structures and operational safety. One example is the fatigue of rails and other train components due to increased axle loads and changes in train speed. Another noteworthy point, still related to changes in load and speed, is the risk of train derailments. All these problems can have a severe impact on the cost of the operation.

Railroad Instrumentation

The purpose of wagon instrumentation is to identify the points and regions of the railroad that cause the most damage to the trains. Knowing these areas makes it possible for management to make timely and assertive interventions to increase the useful life of both the vehicles and the permanent way. In order to collect the quantities involved in the operating process, an on-board instrumentation system is required, which can contain measuring devices such as: accelerometers, strain gauges, pressure sensors, temperature sensors, displacement sensors, GPS equipment, etc. The system is able to collect the output data from the sensors - understanding the dynamics of the wagon; issue alarms and associate them with its global positioning - the latter monitored by GPS (Figure 2).

Figure 1: Global alarm identification [2].

Measuring the deformation of wheelsets, using the extensometry technique for example, makes it possible to know indirectly the lateral (L) and vertical (V) loads (Figure 3) to which the train is subjected along the track. By measuring wheel loads, it is possible to accurately quantify peak load events during a journey. These events, which can cause derailments, are usually associated with significant changes in the track path (small radius curves), excessive speed of the wagons, or even sudden braking events (emergency stops) of the trains. Figure 4 shows the derailment mechanism to which the condition defined by Nadal applies.

Figure 2: Lateral (L) and vertical (V) loads - [3] Adapted.

Figure 3: Derailment mechanism according to Nadal [3].

Once the L and V loads of an operating route are known, it is possible for engineering to associate premature component wear and reduce the risk of derailment events by determining the L/V coefficient. Figure 5 shows a graph constructed from data measured in the field.

Figure 4: L/V coefficient during a loaded cycle - [2].

The technique of instrumentation on railroads, using sensors to study and understand the quantities, requires the correct specification and use of sensors and data acquisition devices, since the choice is associated with factors such as: what data is expected by the requester, how many journeys will be monitored, what duration and distance will be measured, what will be the format of presentation to the client, among others. 

In addition to measuring quantities using sensors and cameras, which can be seen in more detail in the article: Vibration analysis using image processing, and issuing alarms to the requester, it is possible that data such as deformation can be applied to studies using the Finite Element Method (FEM). This study will enable the development of component fatigue analyses (shock and traction devices, tricks and wheels, for example), with the aim of estimating their useful life in cycles for the customer's specific and known operating conditions. 

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References:

[1] Associação Nacional dos Transportadores Ferroviários – ANTF. Disponível em: <https://www.antf.org.br/informacoes-gerais/> 

[2] Kot Engenharia Collection. 

[3] DALLY J. W., Experimental stress analysis, McGRAW-HILL, 3rd ed., 1991.

[4] AAR, Manual of standards and recommended practices. Design, fabrication and construction of freight cars, section C part II, 2011.