ADHESION, CREEPAGE AND WEAR IN WHEEL-RAIL CONTACTS (PLASTICITY, CONTAMINANT, FRICTION)

Utilizing the extensive experimental data from the IIT-GMEMD 1:4.5 scale wheel rail simulation facility, the hyperbolic tangent is suggested as the continuous functional constitutive relation for the adhesion-creepage of steel-on-steel rolling contacts. This involves two fundamental properties, the critical adhesion coefficient and the critical creepage. Based on the relation, the adhesion behavior of contacts, for combined longitudinal and lateral creepages, is derived. The experimentally observed influence of the lateral creepage on the slopes of the longitudinal adhesion-creepage relation is established for the first time. The analysis is extended to the more complex two contact interaction of a flanging wheel. Influence of important parameters on the tractive capabilities of wheel-rail contacts is considered. Distinctly recognisable effects of the tread and flange contacts are highlighted and it is concluded that the flange can contribute up to 65% traction on curves. Flange lubrication has serious deleterious effects on adhesion during curving. Correlation with experimental data is generally good.;The study points to the urgent need for redesign of wheel and rail profiles. Controlled laboratory experiments should form an important phase of such efforts. It is concluded that the adhesion-creepage analysis and the experimental wear data should be integrated in terms of the energy aspect of contacts to close in on the problem of profile degradation of wheels and rails due to plasticity and wear.;Hertzian experimental data showing the influence of axle loads, applied traction and use of sand on wheel/rail wear are reported. Wear is observed to increase sharply beyond limiting values of (i) axle loads corresponding to an initial contact stress termed 'Threshold Stress' and (ii) adhesion coefficient = 0.25. These are significant design parameters. Wear increases by one to two orders of magnitude when sand is employed in contacts to improve adhesion. Test data from geometrical simulation tests include the influences of parametric variation of angle of attack and the ratio of lateral to vertical loads. An all inclusive wear index termed 'Severity Index' is found to correlate well with the wear data. This can be employed for wear predictions.