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High-order polygonal wear of wheels is one of the most severe technical challenges for China's high-speed trains at present, and its formation mechanism has not been thoroughly understood. The effect of train traction on the wheel polygonal wear of high-speed trains was studied based on a wheel/rail rolling contact finite element model. The frequency domain characteristics of unstable vibration of the wheel/rail system under rolling/sliding contact were studied by using the finite element complex modal analysis method. We also examined wheel/rail contact forces and friction in the time domain. The cause of the high-order polygonal wear of Chinese high-speed train wheels was revealed. The effect of the vehicle speed and the wheel diameter on wheel polygonal wear were investigated. The results show: the friction-induced vibration of the wheel/rail system will be excited when the rolling/sliding contact between the wheel and rail. The radial zoom modal of the wheel is an unstable mode, which is the main cause of the 21-22 order polygonal wear of the high-speed train wheels in China. Additionally, vehicle speed has a linear relationship with the order of polygonal wear. Reducing the vehicle speed helps to control the polygonal wear of the wheels. Wheels of different diameters exhibit varying degrees of polygonal wear, with smaller wheels being more resistant to friction-induced vibrations. [ABSTRACT FROM AUTHOR]

• A 3D FE model of wheelset-turnout-sleeper structure is established. • The ratcheting effect of turnout material is simulated. • A mixed implicit-explicit FE method is used to simulate the wheelset passing through the turnout. • The transient contact behavior of high-speed turnouts under cyclic loading is investigated. • The evolution of ratcheting strain of rail under different numbers of cycles and crossing speeds is discussed. The present work introduces a three-dimensional finite element model for the wheel-turnout-sleeper system, incorporating a cyclic constitutive model that accurately captures the nonlinear hardening behavior of rail steel under cyclic loadings. At the same time, a mixed implicit-explicit finite element method is employed to investigate the transient rolling contact behavior of wheel-turnout. Through dynamic analysis, the transient rolling contact status of the wheel-turnout, stress and strain responses of the turnout, and wheel-rail forces are investigated under varying crossing speeds and number of cycles. It is found that during the wheelset crossing, the contact stress remains relatively stable on the stock rail, and multi-point contact occurs at the wing rail and long point rail, and the contact stress on the surface of the long point rail is more significant. With an increase in crossing speed in the same cycle, there is a gradual rise in contact stress on the long point rail face. At the same crossing speed, with the increase in the number of cycles, the contact position between the wheelset and the long point rail gradually moves back, and the top width of the contact position gradually expands. Meanwhile, the fluctuation range of vertical displacement of the wheel center diminishes, and the wheel flange moves away from the long point rail. Additionally, a progressive accumulation of ratcheting strain is observed on the rail, and the ratcheting strain on the long point rail significantly exceeds that on the stock rail. The research results will help to provide a reference for the optimization and design of the critical cross-section profile of the long point rail and will have guiding significance for the maintenance and repair of turnouts. [ABSTRACT FROM AUTHOR]

A numerical method for the fast evaluation of ratcheting in solid-contaminated contact between rollers was developed. The physical problem was simplified with a plane-strain half-infinite body, with a distribution of pressure and tangential stress on the contact surface obtained by considering the presence of evenly spaced solid contaminant particles between the contacting bodies. Such a distribution was obtained by an analytical method, which considered the material of the contacting bodies as linear elastic. The stresses under the contact surfaces were calculated using the Boussinesq-Cerruti model. Subsequently, the plastic strain accumulated in the roller after each application of the contact load was calculated by means of a non-linear kinematic-hardening constitutive law, also considering the effect of wear in removing material layers from the surface. First, the effects of the introduced approximations were evaluated. In particular, the error in calculating the plastic strain using contact load distributions from a theory based on linear elastic behavior was evaluated by comparison with the results of finite element models. Subsequently, the method was used to assess the experimental results of previously published studies on sand-contaminated contact between rail and wheel materials. Despite the approximations and indetermination of some model constants, the method was proven to be able to qualitatively explain many of the damage mechanisms related to the interaction of the contacting bodies with the contaminant particles. • A numerical method for assessment of solid-contaminated contact was developed. • A contact pressure distribution with solid particle contamination was assumed. • The cyclic plastic strain was calculated by a non-linear kinematic-hardening model. • The error due to the approximations was evaluated. • This is a valuable tool for comparative design for ratcheting and wear damage. [ABSTRACT FROM AUTHOR]

A novel internal rotor bend actuator is presented that enables compensating strains to be applied about the rotor centre. Axial reaction tubes are used to maintain the structural stability of the bend actuator and to provide feedback on the level of actuation. The system is powered by an onboard battery and the actuation is derived from the operation of lead screw motors. The actuation is commanded wirelessly, thus providing the functionality for an autonomous rotor. The integrated rotor is demonstrated in isolation via laser tracker measurements and for the rotating prototype system. Actuated bending gave rise to radial displacements at the central point relative to shaft ends of approximately 50 µm peak-to-peak. These results validate a finite element deformation model. The rotor was levitated on active magnetic bearings, then rolling elements bearings, to demonstrate the synchronous vibration control achievable by static internal bending. The potential now exists for the commanded actuation to compensate for rotor eccentricities arising from manufacturing errors and dynamically induced unbalance for the cancellation of underlying synchronous vibration. • Novel structure bending concept. • Design of an experimental prototype. • Experimental validation of bending capabilities. • Results matching with finite element modelling. [ABSTRACT FROM AUTHOR]

The rail is subjected to cyclic stress and plastic deformation, excessive accumulation of which can promote rail degradation. A finite element (FE) model of three-dimensional (3D) cyclic rolling contact (CRC) with the implementation of an improved cyclic plasticity constitutive material model is developed to analyze the 3D elastic–plastic stress. Comparisons of the FE simulation results of 2D repeated moving pressure (RMP), 3D RMP, and 3D CRC models are conducted to elucidate the differences. The evolution and distribution patterns of the elastic–plastic mechanical behavior of wheel–rail contact with the number of cycles are also investigated. The FE results show that the 2D RMP model is conservative in predictions, and the results derived from the 3D RMP and 3D CRC models are comparable, while opposite results are available for some essential components. The 3D CRC model is a necessary choice especially for fatigue life prediction study. Due to the partial slip and cyclic rolling, the stresses and strains near the rail surface layer are significant and continuously accumulate. The residual equivalent plastic strain and the ratchetting strain increase with the increase of the tangential traction and the axle load, which will accelerate rail damage. • A 3D cyclic rolling contact FE model is proposed to study elastic–plastic stress. • Validation of the improved cyclic plasticity constitutive model by experiments. • FE simulation results and necessity choices are compared for three models. • The evolution of residual stresses and ratchetting strains in rail is revealed. [ABSTRACT FROM AUTHOR]

Tire design with respect to vibrational behavior and noise emission is a challenging task due to the large number of parameters and their coupling. Therefore, accurate high fidelity nonlinear Finite Element (FE) models are needed to aid in the design process. The widely used Arbitrary Lagrangian Eulerian (ALE) models, despite their computational efficiency, are limited to rib-slicked tires and require significant effort to consider inelastic material behavior and frictional phenomena. To overcome these limitations a novel nonlinear FE tire model is presented based on the Total Lagrangian (TL) formulation. The TL model is compared to the reference ALE model for the case of stationary rolling on a smooth and a rough road surface. The observed match of the TL model with respect to the hub and contact forces proves the feasibility of using the TL formulation in the context of rolling contact tire simulations. Therefore, the TL model can be seen as a valid alternative to the frequently used ALE models. • High fidelity nonlinear Finite Element models are required in the tire design process. • The Arbitrary Lagrangian Eulerian formulation poses limitations in modeling. • A nonlinear Finite Element Total Lagrangian tire model is presented. • The behavior of the Total Lagrangian matches the Arbitrary Lagrangian Eulerian model. [ABSTRACT FROM AUTHOR]

The adhesion at the wheel-rail contact is critical in train operation. Low adhesion leads to a longer distance for a train to accelerate and brake, and this may cause serious accidents. Sand particles are applied onboard trains at the wheel-rail contact to enhance the adhesion level. In this study, a finite element model is developed to investigate the mechanical behaviour of sand particles in a wheel-rail contact and how they affect the adhesion level. The acceleration and braking events using rolling/slipping and sliding contacts are simulated. Morphological properties of sand particles such as size and aspect ratio are considered. The adhesion enhancement is quantified from each simulation for comparison. The results indicate that the adhesion enhancement during the first contact between the wheel and sand particles is negligible and starts to increase when the wheel is rolling on the fragments. Its magnitude is controlled by the new third-body layers generated during the particle breakage under both rolling and sliding contacts. However, under sliding contact, when a similar amount of fragments is considered, the coarser particles with a larger aspect ratio tend to produce a higher adhesion enhancement. • Adhesion enhancement by sand can be correlated to newly generated surface area of third body. • Sand provide a higher adhesion enhancement during the acceleration compared to the braking. • During traction, the adhesion enhancement is influenced by the number of fragments. • During braking, the coarser and elongated particle generates a higher adhesion enhancement. [ABSTRACT FROM AUTHOR]

• The model can account for the non-linear lifting of the flange groove and the effects of wheelset traverse and side roll. • The wheel tread and flange are alternately loaded with two wheel load transition areas in the frog area. • Wear in the flange bearing area is significantly higher than in the tread bearing area, with an increase of 59.7%. • RCF damage dominates in the wing rail and the two wheelload transition areas. • Reducing the speed to 15 km/h significantly improves the service performance of the fixed frog. The tram No. 3 turnout fixed frog uses a variation in the depth of the flange groove so that the wheel rolls over the frog area in a continuous flange bearing. This method of travelling over the turnout requires the wheel load to transition back and forth between the tread and the flange, resulting in wheel-rail impact, which in turn affects service life. In order to investigate its service characteristics, this paper has established a transient wheel-rail rolling contact finite element model for the No. 3 turnout fixed frog. The macroscopic dynamic response and microscopic wheel-rail contact solution as the tram passes through the turnout at different axle weights and speeds are analysed in detail, and the changing patterns of wear and fatigue damage are investigated. The research shows that rail wear is particularly severe in the wheel flange bearing area, approximately 1.6 times greater than in the tread bearing area. In addition, when tram speeds are reduced to 15 km/h, there is a significant reduction in wheel-rail impact and wear, thereby improving ride smoothness and safety. The results of this study are of great significance to the operation and maintenance of the No.3 fixed frog turnout. [ABSTRACT FROM AUTHOR]

[Display omitted] Material microstructure plays a key role in crack initiation under rolling contact fatigue. When studying microstructure with crystal plasticity finite element method (CPFE), mesh sensitivity study is of great importance, as the surface-near region is under high uniaxial stresses. In this paper, a new structured mesh strategy is purposed and compared with the classical unstructured mesh strategy. Modelling tests on a bi-grain and a polycrystal model show the calculation of geometrically necessary dislocation (GND) density, recently proposed as a suitable fatigue damage indicator, is highly dependent on mesh morphology, when GND hotspots tend to appear near distorted elements even in homogeneous materials. With uniform mesh size and shape, structured mesh elements can provide physically more acceptable GND calculations, which is particularly important in loading scenarios with complex stresses, such as rolling contact fatigue. Computational efficiency is also improved compared to unstructured models because a smaller number of elements are required in a structured mesh model and pre-processing of the mesh is not required. [ABSTRACT FROM AUTHOR]