An Analysis Of The Transient High-Speed Wheel-Rail Rolling Contact In The Presence Of A Wheel Flat

Wheel-flat is the earliest damage type of wheel tread known by human. As yet, rapidly developing of high-speed and heavy haul railway, it is still one of major factors causing out-of-round of wheel. Through a valid 3D transient FE model which included 3D flat geometries, this thesis systematically studied transient rolling contact in presence of wheel-flat, and corresponding high frequency interaction of vehicle-track coupling dynamics in high speed.First of all, it simply introduced the engineering background and literature review of wheel flat, plus pointing out the necessity of a 3D transient FE model in order to study wheel flat.Secondly, a detailed introduction was made to this 3D rolling contact FE model. Based on this model, transient rolling contact solution was acquired by simulating Chinese wheel-rail system called LMa-CHN60 with smooth running surface. In addition, this model was validated in the view of creep force/creepage curve by comparing with the well-known CONTACT code.By employing this valid FE model in chapter 3, detailed rolling contact solution in presence of wheel-flat showed that it might appear two-point contact or contact loss while running in different speeds, accompanying with the state of full slip. Compared with multi-rigid-body dynamics, this model accounted for mass distribution of wheel-rail and elastic deformation, which yielded a much higher critical speed.In chapter 4, through introducing measured elasto-plastic material which concerned strain rate effect (SREEPM), it analyzed in detail the difference of transient rolling-contact solution between elasticity and elasto-plasticity. Compared with elastic material, the large effective stress occurring in the edge of wheel-flat would dropped dramatically due to plastic flow. Residual stress belonging to shocked SREEPM leveled lower than that of smooth surface, which might give rise to an extinctive influence after a second rolling contact.Following chapter 4, the author suggested a new general method achieving the division of adhesion and slip area, especially for velocity dependent friction (VDF). Comparing with Coulomb friction, VDF would affect significantly impacting phenomenon.In the 6th chapter, parametric analysis was carried out, including the variation of axle box acceleration (ABA) with flat geometries and operation velocities, which provided a database between ABA signal and flat for on-line automatic detection system. Comparing with smooth case, wheel-flat could arouse two main frequencies of 1099 Hz and 1798 Hz in terms of ABA. These two frequencies would increase notably with the increase of flat size, which could be used for judging damage extent of wheel flat. ABA and normal force became larger due to a larger flat size, achieving their maximum in the speed section between 150 and 200 km/h.In the last, conclusions and outlooks were provided.