Ultrasonic assessment of wheel—rail contact evolution exposed to artificially induced wear

Abstract

One of the most important effects that wear originates on the wheel-rail system is represented by the significant changes introduced in contact area features and contact pressure distribution. In fact, in most cases, even regular operation gradually modifies the profile of the contacting elements so as to transform the original Hertzian counterformal conditions into a conformal contact characterized by lower average pressures and relevant alterations in the size and shape of the contact patch.On the basis of the aforementioned considerations, this study presents the results of a series of experimental tests carried out with an ultrasonic non-invasive technique, with the final purpose of assessing to what extent wear induces modifications in contact parameters. To this end, in a regular flanged wheel, increasing degrees of wear were artificially produced at the centre of the tread. The interface of the wheel-rail systems thus obtained was investigated with highfrequency ultrasonic waves and the observed coefficient of reflection (which is known to be related to contact conditions) was graphically processed to build contact maps from which to extract information about the size and shape of the contact area and pressure distribution.The results allowed the monitoring of the transition from counterformal to conformal contact, and helped to establish an empirical relationship between the amount of wear and both the contact area value and average pressure. Moreover, contact pressure distribution (obtained with a dedicate calibration procedure) showed that conformal contacts lose the original 'one-peak' pressure trend and exhibit a multi-peak configuration. Thus, the ultrasonic method confirmed its capabilities to faithfully monitor contact conditions even in the case of randomly altered geometries of the contacting elements and, in the specific case, may represent an effective tool in validating the wear simulation models.

In situ evaluation of contact stiffness in a slip interface with different roughness conditions using ultrasound reflectometry

“…Recently, ultrasonic techniques have been used to observe the contact between wheel and rail [14][15][16][17][18][19][20][21]. Though there are spatial resolution limits and considerations of transducer positioning to ensure the sound waves reflect off the area of interest, this technique can be used to non-invasively and directly observe the contact.…”

Modelling verification and influence of operational patterns on tribological behaviour of wheel-rail interaction

“…To address such a challenge, considerable efforts have been made on devising new methods/devices during the last decades. For instance, in [11,40,41], an ultrasonic noninvasive method was successfully used to estimate the dimension of the contact patch and the resulting normal pressure in the laboratory test. Also, several on-board [10,42,43] and trackside [44] field measurement devices were developed to predict the wheel-rail contact forces and/or the accelerations.…”

Transitions in rolling-sliding wheel/rail contact condition during running-in

“…Practical implementation is also difficult because the film disintegrates under the high-pressure and shear between the wheel and the rail. Recently, ultrasonic techniques have been used to observe the contact between wheel and rail [16][17] [18] [19] [20]. Though there are spatial resolution limits and considerations of transducer positioning to ensure the sound waves reflect off the area of interest, this technique can be used to non-invasively and directly observe the contact.…”

“…The proportion of the wave reflected depends on the stiffness of the contact [21] [22]. This approach has been used to determine the contact pressure distribution in wheel-rail contacts and the influence of wear, roughness and surface defects on the contact patch [17] [19]. This actual distribution of the contact pressure could apply to the simulation of wear amount and damage propagation with consideration for surface topography [23] [24].…”