Study On Coupling Relationship Between Rolling Contact Fatigue And Wear Of Wheel-Rail And Prevention Measures

The rolling contact fatigue and wear of wheel-rail become more and more serious with rapid development of the heavy-haul and high-speed railway in our country. They are becoming an important influencing factor on transportation safety of railway. So, the studies on the mechanism of the contact fatigue and wear of wheel-rail and preventive measures have important guiding significance for alleviating the damage of wheel-rail, increasing the economic and social benefits and of railway transportation.The rolling contact fatigue and wear behaviours of wheel-rail have been investigated under unlubricated condition using JD-1 wheel/rail simulation facility and a reciprocating rolling wear testing apparatus with the help of optical microscopy (OM), laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM). The effect of wear rate on fatigue crack damage has been analyzed in the rolling wear of wheel-rail process. The effects of rail base slope, rail gauge and curve radius on the wheel-rail contact patch behaviours have been analyzed using the rolling contact theory of three-dimensional elastic bodies with non-Hertz form and numerical program CONTACT. The differences of prevention measures of fatigue and wear rails have been studied in detail. Main conclusions are drawn as follows.1. The increase of brake force, creep ratio and axle load lead to the increase in wear volume of wheel. The wear mechanism of wheel steel could accompany a transition from mild abrasive wear to severe adhesive and fatigue wear with the friction force increasing, which result in the initiation of fatigue crack and white layer, and then aggravate plastic deformation and fatigue spalling on the wheel roller surface. The carbon content of material has no effect on rolling friction coefficient of wheel steel, but wear mechanism of wheel steel depends strongly upon carbon content of material. Decreasing carbon content of wheel steel may alleviate fatigue spalling damage evidently, but could increase the wear volume of wheel rapidly due to poor wear resistance of material.2. The strength character and wear resistance of PD3 are superior to U71Mn rail's. But U71Mn rail has better fatigue damage resistance and resistance to fatigue crack growth. The fatigue crack would initiate along the direction of plastic deformation and grow toward depth direction along a sharp angle. There are two types of different crack growth forms. Increasing axle load, decreasing curve radius and application of brake force would increase wear volume of rail, aggravate fatigue damage and plastic deformation of rail roller. The probabilistic model of fatigue crack growth rate with a random variable is established. By means of maximum likelihood method of estimation, the upper limit values of fatigue crack growth uncertainty equations of rail material are given under the probability condition. The results indicate that the uncertainty equations of fatigue crack growth rate have a good agreement with the testing results.3. The forecasting model of rail wear volume using BP neural network is established. The results indicate that the BP neural network forecasting model has high prediction accuracy. The trained BP neural network model has been used to forecast the effect of test parameters on rail wear volume. The results indicate that the speed, angle of attack of wheel-rail and axle load have different influence laws on rail wear volume.4. The investigation on rail fatigue oblique crack and side wear volume on the Guangzhou-Shenzhen high-speed railway shows that when side wear of rail is severe, the rail fatigue oblique crack is slight. The relationship between rolling wear and fatigue damage of wheel-rail is manifested as mutual competitive and restrictive coupling mechanisms. That is to say, while the wear is serious, the fatigue damage is relatively slight. On the contrary, while the fatigue damage is serious, the wear is slight. In the practical application, increasing wear rate can alleviate fatigue crack damage of rail and prolong the fatigue life.5. The contact behavior of wheel/rail of worn wheel tread is not achieving the optimal state when the rail base slope is 1/40. So, it is suggested that the profile of worn tread is optimized over again. The increase in rail gauge can change contact geometrical parameters of wheel-rail, creepages, contact stresses and stick-slip areas of wheel-rail contact patch. Decreasing curve radius would make longitudinal and spin creepages, friction work and total slip of wheel/rail contact patch increase rapidly, minish stick area of wheel/rail contact patch. Especially for the high-speed railway, it is suggested that the curve radius should increase as far as possible in the curved track design process.6. The wear and the plastic deformation are dominant for heavy-haul curve rail. However, the damage of high-speed rail is fatigue mainly. The wheel-rail lubrication, wheel profile and rail grinding of heavy-haul and high-speed railway would present very great difference due to the difference of rail damage. On the basis of the coupling relationship between fatigue crack damage and wear, the curve railhead asymmetrical grinding of high-speed railway is given. Moreover, it is different from the curve railhead asymmetrical grinding of heavy-haul railway. The results indicate that the asymmetrical grinding can prevent and alleviate effectively the formation and development of rail oblique crack damage. The selection requirements of rail material of heavy-haul and high-speed railway are not the same. Rail material should be selected and used according to practical rail damage.