Analyses Of Transient Wheel-Rail Rolling Contact On Curves

Higher speeds, heavier axle loads and the booming of urban railways, which usually include many small radius curves, lead to more and more rail damages occurring on curves. Therefore, it becomes increasingly important to study the transient wheel-rail rolling contact on curves. With the rapid development of computer technology, it has become feasible in recent years to solve the wheel-rail rolling contact using the finite element method. Previously, static calculation of finite element method were usually used to solve the wheel-rail contact on curves, a half wheelset and a straight track were normally assumed to reduce the model size, and the curving was typically simulated by applying different lateral displacements and angles of attack. This thesis targets at developing a more accurate explicit finite element model to analyze the curving of a wheelset in the time domain, with the final purpose on understanding the rail damage on curves.Using ANASYS/LS-DYNA, a 3-D transient wheelset-rail rolling contact model has been developed in this thesis to study the curving behavior of a wheelset on curves of a Chinese metro line. The continuum vibrations of the wheels, axle and rail, the longitudinal, lateral and spin creepages, and the structural vibrations of the system are all taken into account. With such a model, the transient rolling behavior of a smooth wheelset on smooth rails of curves is first reproduced numerically in the time domain. Parameters like the radius of curvature, speed, lateral displacement, and traction and friction coefficients are varied to analyze their influences on the transient wheel-rail interactions, and the focus of analysis is placed on the rail head frictional work.From the results of smooth wheels and rails, it is found that in steady-state curving, with the decrease of track radius (the radius range from infinity to 300 m), the torque guiding curving of the wheelset increases, the wear of the outer rail increases, while the wear of the inner rail decreases. Moreover, the wear difference between the inner and the outer rails increases, correspondingly. For a case with cant deficiency, i.e. at a speed higher than the equilibrium speed, lower rail wear is expected on curves. A very large lateral displacement for the wheelset (in the range is 0-8 mm) can significantly increase the contact force, contact stress and frictional work of the outer rail, and further its wear and damage. A larger traction coefficient (the variation range is 0-0.3) leads to higher wear rates of rails, and the wear difference between the inner and the outer rails is increases with the traction coefficient. In a case without traction, the lubrication applied on the top of the inner rail can reduce the wear of both rails, but in the case with a large traction torque, the low friction coefficient on the inner rail can actually increase the wear rates.Rail corrugation on curves of the metro line is simulated by the above-developed FE model to study its influence. The corrugation is only applied on one rail for simulation in this work, i.e. unilateral corrugation is simulated, and the focus is placed on the difference between the dynamic interactions on the two rails. For corrugation with the wavelength of 40 mm, it is found that when the corrugation occurs on the outer rail, the wear of the un-corrugated rail is more uneven at 30 and 70 km/h than at a speed between 40 and 60 km/h. When the corrugation occurs on the inner rail, the uneven wear on the un-corrugated rail is relatively low at 40-50 km/h. The variation of the frictional work on the un-corrugated rail is slightly larger in the case with the corrugation on the inner rail with respect to that with the corrugation on the outer rail. When corrugation with the wavelength of 160 mm exists, the uneven wear on the un-corrugated rail reaches its maximum at 40 km/h, and the variations of tangential force and frictional work is larger in the case with the corrugation on the outer rail than those with the corrugation on the inner rail.Through introducing a strain rate dependent elastic-plastic material model measured by a high strain rate testing system, the transient wheel-rail interaction at an initial state before work hardening is analyzed. It is found that the contact patch is larger in the elastic-plastic condition than that in elastic condition, resulting in smaller normal and tangential contact stresses due to more conformal contact geometry. Significant residual stresses and strains come into being after the pass of wheelset. Moreover, the results of frictional work showed that the wear rate should be lower under that elasto-plastic condition.Finally, conclusions are drawn and discussions about future work are given.