Research on fastener lateral nonlinear stiffness characteristics and its impact on wheel-rail stick-slip vibration

Accurately modeling fastener lateral dynamics and its parameters is crucial for predicting stick-slip vibrations on curved tracks and rail corrugation defects. Nonetheless, the complex lateral force transmission within fasteners, leading to nonlinear stiffness characteristics, poses a challenge to the accuracy of conventional linear spring-damper models like the Kelvin-Voigt model (KV model) in representing the true behavior of fasteners. Hence, this study presents a theoretical dynamic model that incorporates the nonlinear lateral stiffness characteristics of fasteners and investigates its impact on wheel-rail stick-slip vibrations. Using segmented fasteners employed in subway systems as a case study, a series of indoor experiments is conducted to evaluate the nonlinear lateral stiffness characteristics of the fastener system. Then through finite element simulations of lateral force transmission in fasteners, these characteristics are classified into three stages: shear, slip, and collision, with a particular focus on the influence of elastic pad friction coefficients at each stage. Subsequently, A theoretical dynamic model for fastener lateral stiffness is developed by combining the Kelvin-Voigt model with the Berg friction model. This model is integrated into a vehicle-track spatial coupling model to formulate a predictive model for wheel-rail stick-slip vibrations on curved track sections. Lastly, the model's accuracy is verified for a specific operational scenario involving a subway curve segment by comparing measured rail displacements with simulation outcomes. Furthermore, the study explores the impact of nonlinear lateral stiffness characteristics of fasteners on wheel-rail stick-slip vibrations. The findings indicate that the occurrence of lateral slip in fasteners markedly decreases lateral damping, leading to high-frequency oscillations in rail stick-slip forces. Consequently, it is recommended to prevent fastener lateral slip during service operations.