A technique to charactererize the wheel-rail interaction by means of a diagnostic railway vehicle

Damage mechanisms such as surface cracks, plastic deformation and wear can significantly reduce the service life of railway tracks and rolling stock. They also have a negative impact on the rolling noise as well as on the riding comfort. In the study of the interaction forces which act in the wheel-rail contact point and the oscillatory motions to which the vehicle is subject during the running, different parameters have been introduced to quantify the vehicle safety against derailment, its aggressiveness toward the track and the passenger's comfort. For each of these parameters, associated to the vehicle or track status, a threshold value has been defined according to the experience and the statistical distribution of the faults, more than to a strict analysis. If all the parameters exceed their threshold value, the vehicle safety can't be guaranteed. Therefore, it is advisable to develop test methods that consider the simultaneous faults on the railway track and on the vehicle axle. The opportunity to employ diagnostic vehicles able to measure simultaneously all the parameters related to the track and wheel geometry allows us to characterize the real wheel-rail interaction, rather than simulate this interaction using computer-based models. In this paper we will introduce the equivalent conicity parameter, defined in the UIC 518. This parameter will be able to quantify the wheel-rail interaction, collecting all the information related to the wheel and rail parameters. A method to calculate this parameter by means of a diagnostic vehicle will be introduced, validating its accuracy according to the testing procedures defined in the UIC 519.