Theoretical And Experimental Study On Characteristic Of Wheel-rail Contact And Damage Factors Of Rail

The rail damages caused by wheel-rail rolling contact, such as rolling contact fatigue cracks, wear, spalling and so on, become more and more serious with rapid development of high-speed and heavy-haul railway in China. They are becoming an important influencing factor on service life of rail and transportation safety of railway. The problems on rail damages caused by wheel-rail rolling contact are very complex. The investigations in the problems are concerned with many disciplines. Therefore, it is of important realistic significance to study the damage mechanism and development to prolong the service life of rail and improve the security of running train.In this thesis, a finite element model with variable friction coefficient in Wheel-rail rolling Contacts is put forward to finish transient analyses with finite element method. On this basis, the expanding regularity and the influences of rail spalling are analysed. Moreover, the wheel-rail contact fatigue simulation facility under cyclic dynamic loading is invented. The damage behaviors of rail under different wheel-rail contact conditions are investigated by the lab experimentation method. Supported by the Natural Science Foundation Committee of China(Nos. 51236003), the main research work as follows:(1)The studies on characteristics and research situation at home and abroad of rail damage are reviewed. The significance of rail damage is indicated.(2)The parametric variational principle, materials elastic-plastic analysis, contact theory and temperature field analysis are discussed in detail. They provide theoretical guarantees for analysis of wheel-rail contact problem with finite element method.(3)The wheel-rail friction coefficient is measured with pendulum coefficient of friction tester under different temperatures. The relationship curves between wheel-rai friction coefficient and temperature is invited in via the experiment. And on this basis, a three-dimensional thermo-elasto-plastic finite element model of wheel-rail contact is established. The material nonlinear is involved in simulate course. The heat transfer between wheel and rail, the heat-convection and thermal radiation between the rail surface and ambient are taken into consideration in the numerical model. The stress distribution on contact spot and the temperature, stress and strain of rail are analysed under different wheel-rail contact condiyions. The experimental study shows that the friction coefficient decreases with the temperature of wheel-rail contact spot increasing. The numerical result shows that the temperature, stress and strain of rail with constant friction coefficient are higher than the results obtained with the variable coefficient of friction. The axle load has greater effect on rail stresses and strains than sliding speed and rolling speed do.(4)A thermo-elasto-plastic finite element model of plane strain with rail spalling in wheel-rail contacts is established. The temperature-dependent friction coefficient is used in the numerical model. The impact behavior of rail spalling is studied. The influence of the size of rail spalling damage, sliding speed, axle load and constant friction coefficient on the stress and strain of rail is analysed. The simulation results show that the temperature, stress and strain of rail at spalling area are both higher than the results at normal area. The transitory separation between wheel and rail happens when the rail spalling is passed. It makes the load reducing on wheels taken place. The consequence is that the derailment probabilities of train increases and the running safety are threatened seriously. The impact effect between wheel and rail at spalling area strengthen with axle load increasing. The temperature, stress and strain of rail both increase with the increase of axle load and constant friction coefficient. The effect of the sliding speed on the stress of rail is not obvious.(5)Both in China and abroad most of previous laboratory wheel-rail simulation facilities are under static load. The current work designs a wheel-rail contact fatigue simulation facility under cyclic dynamic loading. The effects of wheel oscillations and temperature on fatigue damage and wear of rail are taken into consideration in simulate course. Experimental methods of both micro-scale and macro-scale are used to investigate the influence of different wheel-rail contact condition on rail damage. Based on the experimental data, empirical equation of the variation of the wear loss of steel rail versus vibrational frequency and amplitude of dynamic loads is established. It turns out that normal contact force between wheel and rail, dynamic load and dynamic load coefficient under wheel-rail sliding contact are both higher than the result under rolling contact. The thermal stress near the contact spot under wheel-rail sliding contact is much higher than the result under rolling contact. The abrasion loss and plastic strain of rail under wheel-rail sliding contact are much higher than the result under rolling contact. The rail damage is mainly contact fatigue crack under wheel-rail rolling contact. The rail damage is mainly wear under wheel-rail sliding contact. The maximum of dynamic load and wheel-rail normal contact force increase with axle load and sliding speed increasing.The temperature of rail increases with axle load, sliding speed and vibrational frequency increasing. The abrasion loss of rail increases with the increase of axle load and with the decrease of sliding speed and vibrational frequency. The proposed empirical equation is well forecasting ability. The equation can provide references for the prediction of abrasion loss of rail in the field.