Railway safety is and always was one of the most important issues when it comes discussions made in planning, building and maintain railway infrastructure. Although infrastructure owners throughout Europe keep their tracks in proper conditions to keep the risk of accidents to a minimum, there can be some vehicles on the tracks with too high axle loads or the vehicles are not as well maintained as they could be.
Therefore many countries have built wayside measurement systems that can track overloads vehicles, vehicles with in not perfect shape regarding wheel shape, worn wheel sets and running behaviour of vehicles that could lead to a derailment.
Measurement sites are autonomous local installations which provide information about the running behaviour (e.g. forces, loads, wheel out-of-roundness, etc.) and the noise emission of a passing train. The information about the physical effects of the interaction between wheel and rail is measured by sensors in the track.
Many countries in Europe use Axle Load checkpoints to obtain information about real load distributions in the network. There are also systems to determine the noise emission of rail vehicles. In America such measurement sites are “state of the art”. All cargo vehicles are equipped with RFID systems, making it easy to assign the results to the vehicle. The infrastructure manager and also the owner of the rolling stock and the railway undertaker are very interested to get the results of the measurement.
1. Commercial benefits for the railway system:
Railway undertakers:
- The difference between the payload stipulated in the transport contract and the real load becomes transparent.
Infrastructure managers:
- Improved wheel condition leads to a reduction in infrastructure deterioration (e.g. damage to track and bridges).
- The track access fee can be automatically evaluated including adjustments for overloading, track-friendly and low noise vehicles.
Rolling stock manager:
- The detection of wheel defects extends the service life of vehicle components and reduces the LCC.
- Unexpected failure which can bring a vehicle to a standstill can be avoided.
- The maintenance process can be improved by using condition-based maintenance instead of periodic maintenance.
- Manual inspections (measuring wheel roundness) can be replaced by automatic axle-load checkpoint measurements.
- When monitoring a special fleet of rolling stock it is possible to observe damage trends and tendencies.
- Noise emission can be used as early warning system for vehicle defects
Categorization of interoperable measurement sites
- Instability risk in straight line
- Derailment risk, rail and wheel set loading (stress) in curves lateral wheel forces
- Vertical wheel forces (steady-state and dynamic), overloading
Measurement sites are able to give exact results. These results are however valuable only if they can be linked to the right vehicle, axle or wheel and are properly transmitted and exchanged between the right actors of the system.
Today several countries are working with “Vehicle identification systems” on a national base. The aim for this is to define needs and to harmonize this on a European level.
Some European Railways use different measurement and assessment concepts in the measurements of wheel forces and corresponding quantities. Many of these systems were developed to meet local or national demands. The results from these systems are partly not comparable. The relevant existing standards do not meet all the needs of interoperability. In an on-going trail Austria and Switzerland are already exchanging data provided by measurement sites just before the border to inform the infrastructure owner of the other country in what shape the trains are before passing on to the other country.
2. HRMS – Categorization of interoperable measurement sites
2.1. State of the art
Some European Railways use different measurement and assessment concepts in the measurements of wheel forces and corresponding quantities. Many of these systems were developed to meet local or national demands. The results from these systems are partly not comparable. The relevant existing standards do not meet all the needs of interoperability.
The Goals are to establish an agreement on categorisation (see also result of ALC-Project) of measurement sites and their results related to the standards and requirements of the various customers, for example infrastructure managers, train operators, wagon owners and others, of the data.
2.2. Categorization (Table 1)
Measurement site categories should be defined by the followings:
- Category of risk
- Type of costumers
- Measured parameters, quantities and units
- Required accuracy of measurements
Fig. 1 Head Check, crack initiating from the gauge corner, caused by vertical wheel impact
3. Limit values and assessment concept
The Aim is to establish a set of common limit values and units. Based on these common limit values a common set of rules, interventions and procedures need to be developed. Previous work shows that European Railways use different maintenance and safety limit values, concepts and units. Measurement results from trains running across borders are treated differently. Different assessment quantities and limit values have been defined and different rules, interventions and procedures have been developed based on those limits.
The main aim is the harmonization of assessment quantities and limit values for overloaded vehicles and wheel defects. The work sets out from the findings from INNOTRACK and from UIC work.
The work in in the Limit Value search will focus on vertical (impact) loads (Fig. 1-2). Further, the focus is on safety /risk assessment. The results will provide a technical / scientific basis for limit values. From these tentative limits will be established. Operational consequences of these will be assessed. In addition to giving a recommendation for an alarm limit framework.
Fig. 2 Head cracks due to vertical load impacts
Until now the Results of ALC and INNOTRACK are scrutinized. Conclusions on current practices and deterioration mechanisms are compiled. Results from INNOTRACK are further distilled to extract limit values for “worst case” and “severe case” scenarios. The severity of the phenomenon, influencing parameters, and current measurements and limit values of these parameters are estimated. Information is also collected from relevant research efforts (notably the D-RAIL project).
Focus is set on vertical impact loads and the safety to risk assessment. The goal is harmonization of assessment quantities and limit values for overloaded vehicles and wheel defects (Fig. 3-4)
Fig. 3 Head crack, caused by wheel defects
Fig. 4 Head Crack and Head Checks, caused by traction
The group working on Limit values and assessment concept will provide a technical and scientific basis for limit values whereby the focus is laid on vertical loads and risk of rail breaks, expand to lateral dynamics and risk of rail climb.
3.1. Fracture criterion
To relate fracture to a bending stress, given a certain temperature, the fracture criterion is given as
Here KIt is the stress intensity from temperature loading given by ∆T, which is given as
with T the current and Tn the neutral temperature
KIc is the fracture toughness (including safety factor, influence of brittleness etc).
3.2. Summary of predictive model
For a worst case (regarding time evolution of the contact load) scenario of the three vehicle models, bending moments are predicted for given impact load magnitude and ballast stiffness. Bending stresses and pertinent stress intensities are evaluated for given crack lengths (5, 10, 15 and 20 mm for foot cracks and 25, 30, 35 and 40 mm for head cracks). Thermal stresses and pertinent stress intensities are evaluated for two temperatures (here taken as ∆T = 20 ◦C and ∆T = 40 ◦C) and given crack lengths. Fracture toughness is estimated (here taken as 40 MPa√m) and reduced by the thermal stress intensity (Fig. 5-6).
Fig. 5 Foot cracks for normal track – cold temperatures (40 ◦C below stress free) and an impact load of 350 kN, fracture is likely for a 5 mm rail foot crack if the fracture toughness is 40 MPa√m
Fig. 6 Foot cracks for hanging sleepers – cold temperatures (40 ◦C below stress free) and an impact load of 290 kN, fracture is likely for a 5 mm rail foot crack if the fracture toughness is 40 MPa√m
4. Reproducibility of noise measurements
For the image of the railway system noise is a major topic. The existing noise monitoring systems are based on different methods to determine railway noise. For the cross border operation of rail vehicles a European harmonization of these methods is highly advisable.
There are definite rules for the certification of rail vehicles. The rail vehicles have to be measured on a TSI conform test section; i.e. the acoustic rail roughness, the vertical and lateral track decay rate (TDR) as well as the meteorological conditions have to fulfill the TSI-limits.
For automatic infrastructure noise monitoring systems there are currently no general accepted rules or standards.
In order to guarantee the reproducibility of the noise measurement, the track condition and the ground conditions (acoustic impedance) in front of the detector should be precisely specified in terms of track roughness and track decay rate.
Accordingly, positions of detectors and sensors relatively to the track have to be confirmed (Fig 7/a – 7/b).
Fig. 7/a Control rack for the ARGOS System
Fig. 7/b Acramos for noise measurements
Influence of weather conditions (water on rail, snow, wind) on the validity of noise measurement will be assessed.
The Goals are to test the reproducibility of type testing measurements in service and to measure the noise state of each single vehicle of a passing train by the monitoring site. From these results it is possible to get a general accepted methodology for noise based infrastructure usage charge.
5. Standard for vehicle identification and interoperable output and data transfer
Results from measurement sites are valuable only if they can be attached to the right vehicle, axle or wheel and properly transmitted to and exchanged between the right actors of the system.
Today there are no interoperable rules for the data exchange of measurement results between the traffic operators the train operators the vehicle owners and above all Infrastructure managers. The future herby could lay in the passive or active RFID technology. Camera System have their some weaknesses but could deliver good results in special surroundings.
Both systems are in use in trial installations on the Austrian Railway network.
6. HRMS – the Future
With the end of this project there will be a conclusion of the railway measurement sites in Europe (participants of the HRMS project) as a result of the HRMS Questionnaire. These results will be presented and written in the final report. Then the aim is to find a standard solution to safe and exchange data within the own railway network and even cross border.
References
Elena Kabo, Anders Ekberg, Jens Nielsen & Björn Pålsson: HRMS WorkPackage 2: Limit values, assessment concepts, In preparation.
CHARMEC/Chalmers University of Technology
http://www.charmec.chalmers.se
Fig 1: Anders Ekberg, Bengt Åkesson & Elena Kabo, Wheel/rail rolling contact fatigue — probe, predict, prevent, Proceedings of the 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2012), August 27 – 30, Chengdu, China, pp 29–41, 2012
Fig 3 and 4: Elena Kabo, Anders Ekberg, Jens Nielsen & Björn Pålsson: HRMS WorkPackage 2: Limit values, assessment concepts, In preparation.
Florian Saliger, ÖBB, ALC – Report, ÖBB Documents, HRMS Project Documents
Laurent Schmitt, UIC, HRMS-questionnaire, HRMS Project Documents
Table 1 Key letters for the categorization of Measurement sites
Florian Saliger, Procejtmanager – Research and Development, ÖBB, Vienna, Austria
Laurent Schmitt, Projectmanager – UIC, Paris, France
Wolfgang Zottl, Leader – Research and Development, ÖBB, Vienna, Austria
