Wear-controlled evolution of rolling contact fatigue cracks: A mixed-mode criterion for fish-hook spalling

Rolling contact fatigue (RCF) damage often develops under simultaneous crack growth and material removal, yet the mechanistic interaction between fatigue cracking and wear over service life remains insufficiently quantified. In this work, a coupled experimental-numerical framework is proposed to elucidate wear-controlled RCF crack evolution leading to spalling. Field-measured rail profiles and metallographic observations are combined with multi-body dynamic simulations to determine evolving contact conditions, which are then used as inputs to a three-dimensional fracture-mechanics model incorporating mixed-mode stress intensity factors. The results reveal a characteristic transition in crack trajectory from downward growth to upward turning, producing a fish-hook morphology that precedes surface spalling. The evolution of this trajectory is governed by the magnitude of | K II | at the crack tip, where a stronger shear driving force promotes a more pronounced sliding effect between the upper and lower crack surfaces. As wear progresses, contact migration and stress redistribution increase mixed-mode loading, causing the crack path to rotate toward the surface despite compressive normal stresses. Based on these findings, a wear-fatigue evolution criterion is proposed that distinguishes crack arrest, stable subsurface growth, and spalling-prone upward propagation. Comparison with metallographic sections shows good agreement in crack depth, curvature, and turning location. The proposed framework provides a transferable mechanistic basis for predicting spalling risk and for optimizing wear-based maintenance strategies in rolling contact systems. • Reveals how wear-fatigue competition governs rolling contact crack evolution • Identifies a mixed-mode (K II /K I )-controlled transition to fish-hook crack paths • Proposes a wear-controlled crack evolution criterion for spalling prediction • Validates simulated crack trajectories against field metallography • Provides mechanistic guidance for wear-based damage mitigation