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Content archived on 2024-05-29

Wheelset Integrated Design and Effective Maintenance

Final Report Summary - WIDEM (Wheelset Integrated Design and Effective Maintenance)

The main goal of the WIDEM project was the creation and validation of an innovative and rigorous methodology to design wheelsets. More specifically, the project pursued the following objectives:
- Endurance strength design approach for wheels and axles which will lead to an optimisation of wheelset geometry, a reduction of un-sprung masses and an extension of maintenance intervals while meeting increasing safety and service requirements
- A new wheelset maintenance strategy based on more accurately defined inspection periods through the use of new NDT devices for railway (compensated resonance system)
- Optimise the design and maintenance of wheelsets, to reduce Life Cycle Cost. Wheelset loads will be measured and used to develop design guides for new axles and optimise testing regimes for existing axles
- Increase the competitiveness, capacity and availability of European railway products in the wheelsets area.

The WIDEM project was in principle a re-examination of the basic information necessary to design and validate a railway wheelset and to manage the maintenance parameters that in some way are related its design criteria. The idea of starting this project was stimulated by the application of the new European design Standards. As the verification of full scale fatigue limits of wheels and axles become mandatory, testing methods and interpretation methods of the results were not defined or in general were not homogeneous throughout the European Laboratories.

The new European Standards enable the use of materials different from E1N, but not so much of the latest experience and knowledge in using new material and in designing new advanced vehicles was considered when writing these norms. From a formal point of view, it becomes difficult for the designer to define more precise load spectra and material characteristics that can be accepted by an authority responsible to approve the qualification of a new component.

The project was structured into the following work packages (WP):

WP1 - The accuracy in measuring wheel-rail dynamic loads
Measuring wheel-rail dynamic loads is today a very approximate exercise because of: inadequate technology of the instrumented wheelset (telemetry, data processing and self powering) static calibration of the measuring system which does not reflect the actual service conditions.

The WIDEM project has developed an innovative measuring wheelset made of up to date wireless data processing and transmission technology. A dynamic calibration is performed by using a unique roller rig on which running conditions near to reality can be simulated. A mathematical calibration approach enables to turn the measured strains into vertical, lateral and longitudinal force components by optimising a transfer matrix. The final result is the possibility of improving and verifying the actual accuracy of the measuring system, together with a robust telemetry data transmission system.

WP2 - Wheel-rail load test campaigns
The main task was to collect load data for two different vehicles to be used as a basis for the definition of load spectra. The results are intended to become the basis for defining a common standard method for the definition of wheelsets load spectra to be used in the design and in the service-NDT periodicity evaluation.

WP3 - Improving flexible multibody models to understand the vehicle track interaction
Polimi further developed their flexible multibody vehicle model which is now able take into account the deformability of both the wheelsets and the bogies as well as the car body and the track. While the deformability of wheelsets, bogies and car body is taken into account through a modal superposition approach, the deformability of the track is accounted for through a FEA model of the railroad. Together with concentrated defects, the passage of switches represents the most challenging service condition for the wheelset, in terms of peak values of wheel-rail contact forces. Therefore, the correct simulation of these running conditions assumes critical importance in order to reproduce correctly the extreme values of the load spectra. Also, these are the loading conditions that show the highest sensibility to track flexibility.

From a more general point of view, this modelling work aims to establish the effect of wheel and rail defects on wheel-rail contact forces, in terms of dynamic amplification factors expressed as function of a specific geometrical parameter describing the defect and as a function of speed. Tests performed on the Alstom tilting train will be the basis for the validation of this kind of modelling.

Finally, validated flexible multibody vehicle models should become a tool to evaluate corrections to be applied to nominal load spectra to be used in the design of a wheelset which includes possible high loads that can be found during the life time of this component.

WP4 - The assessment of material properties
The main task was to define a precise procedure to perform full scale fatigue tests on wheel and axles. The reason for this was that different laboratories throughout Europe perform tests in different ways and results are the not always comparable.

Testing experience form the past years plus a benchmark with other laboratories has enabled the definition of all the relevant parameters referred to the component geometry, the measurement of the load, and the statistical evaluation method of the test results.

From a research point of view much work is ongoing to describe better the fretting fatigue phenomena which depends on many parameters that are not carefully considered in the norms: hub thickness (h), interference (i), contact pressure (P), slip (s), axle seat length (L), axle diameter ratio (D/d), axle bending moment (M), nominal longitudinal stress (sigma-n), real longitudinal stress due to bending moment (sigma-r).

WP5 - Development and validation of a new design method for wheelset
With the aim of optimising wheelset geometry, a new design procedure was defined. Taking advantage of new inputs such as life-representative load spectra and actual material fatigue data, first stresses were calculated according to standard principles and then fatigue cycles accumulation theories were added according to endurance design concepts.

WP6 - The probability of detecting cracks in wheelsets
The main task was to establish the POD for different inspection methods and evaluate possible new techniques like the compensated resonance inspection method.

TWI produced POD curves by performing inspection tests on both fatigue tested axles and real in-service cracked axles. Collection of the latter was very difficult, fortunately because it's a very rare event However, axles from service have been collected in the UK and in Germany. Other axles with flaws have been produced in the Lucchini fatigue test rig.

The verified methods were AC, Potential Drop, Phased Array Ultrasonics and Time of flight ultrasonics to size the cracks and then the use of representative on site inspections to establish the probability of detection.

WP7 - The periodicity for in service NDT inspection
This was the final work package in the project and required data from all the other work packages. The WIDEM project aimed to put together all the information that is necessary to perform this evaluation. These include knowledge of the actual load spectra that the wheelset experiences and the material crack propagation properties. Significant work has been completed in deriving crack growth rate parameters under both plane and rotating bending conditions. Finite element analysis have been conducted to aid selection of appropriate stress intensity factors and crack shape development including complex effects such as the presence of the seats in the axle.

The use of a reliability approach to establish periodicity for a given probability of failure is a new development for axle design. Data on loading spectra from other work packages was processed into a format appropriate for the probabilistic model. Consideration of the acceptable target reliability based on historical axle failure data was made and also the potential impact of human error was examined.