Bogie qualification

This is a study case about differents tests that can be performed for a bogie qualification.

DESCRIPTION

As part of qualification procedures on a bogie frame or for investigation purposes, static and fatigue tests are required. These tests are usually carried out in accordance with technical test specifications based on European and/or international standards.

At the request of its clients, our laboratory can take charge of all or part of the essential test stages, on the strength of its COFRAC EN 17025 accreditation, in other words:

Producing the test specification from a set of calculations used to work out the loads to be taken into account and develop the test programme.

Designing and producing the tools needed to simulate limiting conditions representative of the actual conditions encountered in service. During the tests, it is common practice for ancillary equipment such as motors, reduction gears, braking systems, etc. not to be fitted on the frame because of supply problems and/or problems with regard to the space needed for the assembly controls. This is where our laboratory can step in to propose suitably designed interfaces to simulate the presence of these missing parts, while faithfully representing such things as the motor’s axis of rotation, the position of the centre of inertia of the different components, the load directions and the flexibility of the different linkages.
La constitution du plan de jauges peut également nous être confiée. Dans ce cas, nos ingénieurs d’essais, à partir des éléments fournis par le client (calculs) et de leurs propres expériences sur des châssis comparables, déterminent la position des extensomètres à mettre en place en fonction de leur sensibilité particulière aux divers chargements. Le nombre de points de mesure est d’ordinaire de l’ordre de 200 voies mais nos moyens de mesure peuvent traiter jusqu’à 350 voies.

To achieve this, our design office will produce 3-dimension models of the bogie frame mounted on the test rig and find the most appropriate technical solutions with regard to ways of applying the loads, in relation to the client’s needs.

Producing a strain-gauge positioning diagram is a further task that we may be asked to fulfil. For this, our test engineers will work from data supplied by the client (calculations) and dip into their own experience with similar frames to decide on the best positions for the strain gauges to be installed in relation to the sensitivity of these gauges to the different types of load. Generally, the number of measuring points is in the region of 200 load channels but our equipment is such that we can process up to 350.
Performing static tests is a function conducted to test bogie design dimensions by means of stress measurement in order to ensure that the bogie frames are strong enough to withstand both regular and exceptional loads throughout the whole of their life cycles.

Static tests on bogie frames, which are usually performed before fatigue testing, are designed to ensure that:

  •  permanent deformation or disastrous fractures will not occur under the effect of the exceptional loads that may be encountered on a limited number of occasions during frame life cycles,
  • fatigue cracks are not likely to occur under the repeated effect of the normal strains and stresses of everyday operations.

Loads are generally applied by means of static and dynamic jacks with a maximum unit capacity of 400 kN. These serve to simulate the various different load combinations encountered on a bogie frame.

Our control and measuring systems come with software that can automatically process and analyse results.
Fatigue tests are supplementary to the static tests and are carried out to check general design and structural condition.

By measuring some ten different stresses and forces, it is possible to monitor the progress of the tests. Non-destructive testing conducted at predetermined key stages serves to check the mechanical behaviour of the frame.

Fatigue tests consist of reproducing the loads applied to the bogie frame during curving. 10 million curving operations are therefore simulated, alternating between left and right curves every 10 or 20 cycles. The test frequency may be as high as 5 Hz.

Other so-called “specific” forces that tend to exert a local influence on structural fatigue may also be simulated, either at the same time as the main forces or separately. The number of cycles to be performed may vary and depends on the client’s requirements.

For such operations, as many as 14 dynamic jacks may be used at the same time to simulate loads on the bogie frame. Some twenty sensors may then come into play to control and monitor the test. At the Railway Test Agency (AEF), there are two test rigs that can be used for this type of test. As an example, the tests described below have been conducted on behalf of our clients:
  • – Complex inertia test (12 jacks): These fatigue tests consisted of simulating a combination of different loads representative of left-hand and right-hand curving forces, together with the effects of inertia on the ancillary equipment (centrifugal forces; track defects, braking or acceleration).
  • – Traction-braking test (12 jacks): During another operation performed on behalf of a client, the aim was to check that fatigue cracking would not be encountered in traction or braking conditions. Jacks were positioned near the motors to simulate torque. Similarly, reactions at the securing point of the reduction gear connector rod and the longitudinal forces at the axles, which are typically found during acceleration or deceleration, were also simulated.
Non-destructive tests can also be carried out using magnetic particle, dye penetrant or ultrasonic testing techniques (under COFREND accreditation) as part of the fatigue testing process. These tests serve to check that no cracks have occurred during the test process.