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Large magnitude impact loads caused by wheel flats may excite various vibration modes of wheelsets employed in high-speed trains and thereby contribute considerably to the dynamic response of vehicles. In this study, the wheelset is modeled as a flexible body using the modal approach, which is integrated to a multibody dynamic model of the high-speed train coupled with a flexible track slab model. The multibody dynamic model is formulated for a typical high-speed train consisting of a car body, two bogie frames, and four wheelsets. The track is modeled considering the rail as a Timoshenko beam discretely supported on a flexible track slab. The effects of the wheelset flexibility on the dynamic response are illustrated through comparisons with those obtained with a rigid wheelset considering different vehicle speeds and sizes of the wheel flat. Subsequently, the effects of wheel flats on the vehicle–track system are evaluated in terms of the wheel–rail impact forces, axle-box vertical acceleration, and dynamic stress developed in the wheelset due to a haversine wheel flat. The results suggest that the wheelset flexibility can lead to significantly higher axle-box vibration and wheelset axle stress compared to a rigid wheelset in the presence of a wheel flat.

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2010)Development of a vehicle-track model assembly and numerical method for simulation of wheel-rail dynamic interaction due to unsupported sleepers, Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility, 48:12, 1535-1552 To link to this article: http://dx.In practice, it is not very uncommon to find railway track systems with unsupported sleepers due to the uneven settlement of a ballasted track system. These unsupported sleepers are among the major vibration excitations for a train and track system when a train moves forwards on a track. The vibration induced by unsupported sleepers can cause a large dynamic contact force between wheels and rails. For heavily loaded high-speed trains, the deteriorated sleeper support may lead to accelerated degradation of the railway track and vehicle components, and may thus impose safety risk to the operation. This paper presents analyses of a coupled vehicle-track assembly consisting of a roll plane vehicle model, a continuous track system model and an adaptive wheel-rail contact model. In order to improve the simulation efficiency, a numerical approach based on the central finite difference method is proposed in this investigation. The developed model assembly and proposed simulation method are utilised to simulate the vehicle-track dynamic interaction in the presence of unsupported sleepers. The dynamic response in terms of the dynamic wheel-rail interaction force due to one or multiple unsupported sleepers is studied. Important factors influencing the dynamic wheel-rail interaction force in the presence of sleeper voids are also investigated. The results show that the vehicle speed, the gap size and the number of unsupported sleepers primarily dictate the magnitude of impact load which can be significant.

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The dynamic impact forces caused by wheel defects such as a flat have been of primary concern for freight trains operating at high speeds. A pitch plane model of a railway vehicle coupled with a comprehensive three-layer track system model is developed to study impact forces generated at the wheel-rail (W-R) interface in the presence of wheel flats. The W-R interaction is described by the non-linear Hertzian contact spring, while the rail is represented by a continuous Euler beam. The Rayleigh-Ritz method is used to solve the coupled partial and ordinary differential equations of the vehicle-track system. An idealized haversine wheel flat with the rounded corner is included in the W-R contact model. The W-R interface forces are evaluated under single or multiple flats on a single as well as multiple wheels. The forces transmitted to the bearings, pads, and the ballast are also evaluated under impacts due to single as well as multiple wheel flats. The results obtained through parametric analyses are discussed in view of a desirable design and operating condition to reduce the magnitude of impact loads. The results suggest that the rail mass, rail pad stiffness and damping, bending stiffness of rail, and ballast mass affect the W-R impact force considerably, apart from the flat size and vehicle speed. The influence of phase between the multiple flats on the resulting magnitudes of impact forces is also evaluated. The results suggest that the impact loads due to two flats are comparable with those due to a single flat when the spacing between the two flats exceeds 45 • . Furthermore, the magnitude of impact force due to a single wheel flat could be greater than that due to in-phase flats on both wheels, which can be attributed to the pitch dynamics of the bogie.

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Although numerous investigations have been undertaken to study the impact load between railway wheel and rail in the presence of a single wheel flat, little attention was devoted to the case of multiple flats. In practice, it is not uncommon that one wheel develops more than one flat or each wheel on the same axle has a single flat. In this study an adaptive contact model, a two-dimensional roll-plane vehicle model, and a three-dimensional track model are developed to investigate the wheel-rail impact load due to multiple flats. Unlike the commonly used Hertzian contact model, the adaptive contact model takes into account the asymmetry of the contact patch as the wheel flat enters and leaves the contact patch. Two scenarios of multiple flats are considered in this investigation. One deals with two flats on the same wheel defined by their size and relative position, and the other deals with a single flat on each wheel of the same axle. In each case, the induced impact loads are compared with those due to a single flat. The results suggest that the magnitude of impact force attributed to the second flat entering the contact region is strongly affected by the responses due to the preceding flat, depending upon the flat geometry, relative co-ordinates of the flats and the operating speed. The results further suggest that the length of a flat alone, which is commonly regarded as wheel removal criteria, may not be adequate when multiple flats are present.