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Objective In the actual metro construction, it is often necessary to lay turnouts on large-slope sections due to planning and construction constraints, land conservation or topographical limitations. However, it is found through practical application that the large-slope turnout structure leads to poor train stability and ride comfort during operation, thus an investigation on the factors influencing vehicle passing performance through large-slope metro turnouts is required. Method Based on multi-body dynamics theory, using simulation analysis software and taking the No.9 turnout installed on a 30‰ slope as research object, a coupled vehicle-turnout multi-body dynamics model is established. The dynamics performance indicators (including wheel-rail interaction, safety indicators, and stability indicators) of single vehicle passing through large-slope turnout at different operating speeds and friction coefficients are compared，aiming to analyze the impact of various factors on the vehicle passing performance through large-slope metro turnouts. Result & Conclusion It is revealed through simulation research that the impact of operating speed on wheel-rail interaction, stability indicators, and safety indicators is independent of the slope direction during vehicle passing turnouts. When a vehicle passes through turnouts on uphill and downhill slopes, the influence trends of operating speed on the dynamics indicators are consistent, with a more significant impact when going downhill; the friction coefficient greatly affects the wheel-rail dynamic interaction and the vehicle lateral acceleration. As the friction coefficient increases, the wheel-rail interaction force decreases, the carbody vertical acceleration shows no significant change, and the lateral acceleration increases significantly, with a more pronounced effect when going downhill. Therefore, certain strengthening and protective measures should be taken when vehicle going downhill.

Objective When turnouts are laid on slope, the longitudinal force increase on the track due to the cyclic braking of trains will cause uneven rail creeping phenomena， resulting in a more complex stress and deformation pattern for the turnout, and even affecting its normal service. Therefore, it is necessary to study the characteristics of stress and deformation of large-slope turnout rails under cyclic braking loads. Method Tests on fastener longitudinal resistance under CLA (cycling loads action) are conducted, and a non-linear finite element model of the No.9 turnout is established to analyze the turnout rail creeping pattern under CLA. Result & Conclusion The fastener system exhibits resistance degradation under CLA. The maximum creep of the turnout rail occurs after the first train braking. Under CLA, the cumulative increase in rail creeping gradually stabilizes with the increasing number of CLA. The presence of slope will significantly increase rail creeping amount under CLA. The train loading form has minimal influence on turnout rail creeping under cycling braking loads action.

In order to effectively address the engineering problem of optimizing the worn rail profile on subway sharp-radius curves, this paper focuses on the inconsistent wear characteristics of rails on such curves. The contact stress, wheel-rail lateral force, and wear index are taken as objective functions, and key rail profiles at the points of straight-transition, transition-curve, curve-midpoint, circular-transition, and transition-straight are selected. A multi-objective and multi-section optimization scheme based on the optimized limit curve is proposed to design the grinding profile for rails on subway sharp-radius curves. In order to compare its optimization effectiveness, two additional optimization schemes are presented: the second scheme involves multi-section profile optimization with no optimized limit curve as constraints, and the third scheme deals with optimizing a single profile for grinding with equal cross-sections. Through a comparison of the three optimization schemes, the results indicate that all three schemes lead to a reduction in the contact stress, wheel-rail lateral force, and wear index of the outer and inner stock rails after optimization. Scheme 1 shows a more extensive and uniform distribution of wheel-rail contact points, with larger reductions in contact stress and increases in contact area. Scheme 3 only improves contact in severely worn sections, while in less worn sections, the contact distribution becomes concentrated, accelerating wear evolution. Furthermore, in Scheme 1, the cumulative wear after 100,000 and 200,000 cycles is reduced by a maximum of 8.44% and 22.33% compared to before optimization, making it the most effective among the three schemes. Therefore, the optimized profile output by the optimization method proposed in this paper is considered the best solution, which is represented by Scheme 1. [ABSTRACT FROM AUTHOR]

In metro engineering construction, due to the urban planning and construction, economical use of land or the limitation of terrain conditions, metro rail sometimes needs to be laid on the large slope area. When the rail is laid on the ramp, the rail longitudinal force increases on account of frequent train startup and break, resulting in uneven crawling of the switch rail and affecting normal service of the switch. To study the longitudinal stress deformation characteristics of the large lope switch under cyclic loading, a full scale model test on large slope metro switch is conducted to study the deformation law of switch rail under cyclic loading, and the influences of different factors such as the wheel axle load value and the fastener failure on the large slope switch longitudinal deformation. The results show that in the process of single loading-unloading, the rail displacement increases faster and faster with the increase of the load, and rapidly falls back after unloading and produces a residual displacement of 0. 061 mm; under cyclic loading, the maximum longitudinal displacement of the rail during loading and the residual displacement after unloading both increase rapidly at first, then slowly tend to stabilize with the increase of cyclic loading times; after 200 times of cyclic loading, the residual displacement is basically stable at 0.15 mm; the larger the wheel axle weight value, the smaller the longitudinal displacement of rail under cyclic loading and the longitudinal residual displacement of rail after unloading; the more the number of fastener failure, the greater the influence of rail longitudinal displacement and rail longitudinal residual displacement under cyclic loading. [ABSTRACT FROM AUTHOR]

Assembly deviations of wheelsets cause differential wheelset misalignments and change the wheel-rail contact relationship in railway turnouts. In this paper, the motion conditions of wheelsets under the same bogie are analysed with differential wheelset misalignment based on the mechanical equilibrium condition. A rigid-flexible coupling model of vehicle-turnout dynamic interaction that fully considering different misalignment conditions is established to evaluate the wheel and turnout rails dynamic interaction and vehicle dynamic characteristics. The results show that wheelset misalignment can change wheel load transition position and affect wheel-rail contact conditions, especially when the misalignment direction is toward the switch rail. The larger misalignment angle will increase flange contact range and keep the normal contact stress at a higher level. Both misalignment angle and form determine the wheel-rail vertical force. The lateral force is mainly affected by the superposition effect of the eccentric load and the lateral impact of the wheel load transition. [ABSTRACT FROM AUTHOR]

Wheel flat is a form of wheel tread defect that reduces the service life and running safety of trains and tracks. Based on the multi-body system dynamics theory, a rigid-flexible vehicle-turnout dynamic coupling modelwas established, and the wheel diameter-varying flat simulation method used to create wheel flat models of different sizes. The most unfavourable phase of flats on the wheels of a vehicle crossing a turnout was studied by scanning and calculating the phase of the flats. The influence of flat size and vehicle speed on a vehicle with flats crossing a turnout was also analyzed. The results show that, compared with a normal wheel crossing a turnout and a wheel flat acting on the interval rail, a wheel flat acting on the wheel load transition of the frog area will excite greater vertical wheel-rail forces and vertical axle box vibration acceleration; in the turnout area, the main frequency band of the vertical vibration acceleration of the axle box is 550–800 Hz, which is rarely affected by the size of flats or the speed of the vehicle. The third-order bending mode of the wheel is excited when the wheel transits from the wing rail to the point rail. [ABSTRACT FROM AUTHOR]

Laminar plasma discrete quenching of rail surfaces significantly improves the wear resistance of quenched rails by forming a discrete hardened layer on the rail surface, while also introducing residual compressive stress. However, in practice, laminar plasma quenched (LPQ) rails demonstrate numerous fine cracks and spalling at the edges of the hardened layer, potentially threatening the safety of railway traffic. However, most previous studies have focused on the microstructure of LPQ materials and two-disc tests, with few of them including a finite element analysis of the mechanical properties of the quenched rails. In this paper, an ANSYS/LSDYNA explicit finite element (FE) model of the transient rolling contact between the quenched rail and the wheel is developed for the rolling contact behaviour and wear characteristics of the LPQ rail. The innovation of the model is the fact that it takes the inhomogeneous material properties between the substrate and the hardened layer of the rail surface into account, as well as the real residual stress. It was found that the inhomogeneous material properties of the substrate and the hardened layer may be the main cause of micro-cracking at the edges of the hardened layer. Residual compressive stress within the hardened layer has a non-negligible effect on the rolling contact characteristics of the rail. The research methodology in this paper further develops the FE model for LPQ rails, while the results obtained will be important for controlling rail damage. • Developed a model that takes the inhomogeneous material properties and real residual stress into account. • The effect of material inhomogeneity and residual stress on the wheel-rail contact was analyzed. • The effect of material inhomogeneity and residual stress on the wear of laminar plasma quenched rails was analyzed. • Predicted the crack development trend of laminar plasma quenched rail. [ABSTRACT FROM AUTHOR]