Key Takeaways & Executive Findings
- •• A novel non-Hertzian wheel-rail adhesion model is proposed, integrating EHL and extended creep force (ECF) models to capture realistic contact behavior under wet conditions. • The model accounts for surface roughness and elastic-plastic third body layer (3BL) characteristics, improving accuracy over traditional Hertzian-based models. • Validation against high-speed wheel-rail adhesion tests confirms the model's reliability for predicting adhesion in wet conditions. • The study reveals that train speed and surface roughness significantly influence adhesion, with non-Hertzian contact distributions affecting traction and braking performance.
Abstract
Precise solutions for wheel-rail adhesion are important to the traction and braking of the high-speed trains under wet conditions. Current models predominantly rely on Hertzian contact theory assumptions. The present work proposes a novel non-Hertzian wheel-rail adhesion model to clarify the adhesion mechanisms under wet conditions. The non-Hertzian elastohydrodynamic lubrication (EHL) model was developed to obtain wheel-rail normal contact pressure under wet conditions with rough surfaces. The non-Hertzian extended creep force (ECF) model, which considers the effects of pressure and temperature on the elastic-plastic characteristics of the third body layer (3BL), was used to solve the tangential problems based on wheel-rail normal contact results. The numerical model was also validated by the high-speed wheel-rail adhesion laboratory tests. The wheel-rail rolling contact characteristics at different wheelset lateral displacements are investigated. The results reveal that the distributions of normal pressure, film thickness, tangential stress, and temperature show typical non-Hertzian characteristics. Finally, the effects of train speed and surface roughness on the adhesion characteristics are studied at different lateral displacements. The findings show that the present model can be used for the prediction of high-speed railway adhesion characteristics.
1. Introduction
High-speed train operation depends on wheel-rail adhesion for all traction and braking control, representing a complex tribological system governed by multiple interfacial parameters. Lab tests [1–4] demonstrated that wet conditions significantly reduce adhesion coefficients with increasing speed, potentially causing wheel slip, rolling contact fatigue, and increased braking distances. While existing models typically employ Hertzian assumptions for mixed lubrication analysis [5]. Such simplifications introduce substantial discrepancies in both local contact behavior and vehicle dynamics simulations [5, 6]. Therefore, it is essential to develop a precise non-Hertzian wheel-rail adhesion model under wet conditions to elucidate the wheel-rail adhesion mechanism at high speeds.
Recent advances in elastohydrodynamic lubrication (EHL) theory have facilitated the application of mixed lubrication models to study wet condition adhesion characteristics. CHEN et al [7] first developed a three-dimensional wheel-rail adhesion model using the average flow model and micro-asperity contact theory. Later, WU et al [8–11] extended the model to incorporate interfacial fluid effects, rheological properties, micro-scale elastic-plastic deformation, starvation, and thermal factors. While these stochastic models provided valuable insights, they lacked the capability to resolve local contact details. More recently, deterministic mixed lubrication models have increasingly been employed in the study of wheel-rail adhesion. YANG et al [12] developed a 3-D wheel-rail adhesion model under wet conditions incorporating measured surface roughness to analyze braking conditions. WANG et al [13] implemented a transient deterministic model to investigate adhesion under various contamination scenarios. WU et al [14] developed a transient model for high-speed curved track operation under wet conditions. Although these models accurately predict normal contact pressure distributions, they failed to accurately determine the tangential pressure and adhesion curves due to their assumption of constant asperity friction coefficients.
To accurately model the wheel-rail tangential behavior of a third body, MEIERHOFER et al [15] developed a two-dimensional 3BL model treating the interfacial layer as an elastoplastic material. KVARDA et al [16] developed an asperity-based adhesion model combining Kalker’s simplified theory with the third body layer (3BL) representation to determine solid contact friction coefficients. After that, MEIERHOFER [17] extended the 3BL model by introducing the Voce material hardening law and developed a new creep force model called the extended creep force (ECF) model. HUANG et al [18] implemented this approach in a three-dimensional adhesion model integrating simplified EHL theory with the non-Hertzian ECF formulation. Recently, a new wheel-rail creep force model called WILAC model has been developed for estimating adhesion curves with different amount of water on the rail [19]. In the model, the ECF model was used to calculate the adhesion curves in a wider range of normal forces and rolling speeds. A linear regression m
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WU Bing, HUANG Jia-qing, SU Xiang-long (2025). A novel non-Hertzian wheel-rail adhesion model under wet conditions considering surface roughness. Journal of Central South University. https://doi.org/10.1007/s11771-025-6091-3
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Frequently Asked Questions
What is the main contribution of this paper?
The paper proposes a novel non-Hertzian wheel-rail adhesion model that integrates elastohydrodynamic lubrication (EHL) and extended creep force (ECF) models to accurately predict adhesion under wet conditions, considering surface roughness and elastic-plastic third body layer behavior.
How does the model differ from traditional Hertzian-based models?
Traditional models assume Hertzian contact pressure distribution, which is inaccurate for rough surfaces and wet conditions. The proposed model uses non-Hertzian EHL to compute normal pressure and ECF for tangential stress, capturing realistic contact mechanics and improving prediction accuracy.
What are the key findings of the study?
The study reveals that normal pressure, film thickness, tangential stress, and temperature distributions exhibit non-Hertzian characteristics. Train speed and surface roughness significantly affect adhesion, with higher speeds and rougher surfaces generally reducing adhesion coefficients.
How was the model validated?
The numerical model was validated against high-speed wheel-rail adhesion laboratory tests, confirming its reliability for predicting adhesion characteristics in wet conditions.
What are the practical implications of this research?
The model provides a more accurate tool for predicting wheel-rail adhesion, which is critical for optimizing traction and braking control systems in high-speed trains, thereby improving safety and operational efficiency.
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