Fatigue Performance of Engineered Polymer Composite Railroad Ties Under Simulated Railroad Track Conditions

Abstract

The fatigue performance of Engineered Polymer Composite (EPC) railroad ties under realistic track loading and support conditions remains an important consideration for their structural performance and durability. This study evaluated EPC railroad ties manufactured from recycled polymers and mineral fillers through initial mechanical characterization, small-scale fatigue testing, full-scale fatigue testing, post-fatigue mechanical characterization, and forensic investigations. Small-scale specimens were subjected to strain-controlled four-point bending fatigue tests at different strain amplitudes, with extended testing continued for over one million cycles. The full-scale experiment consisted of four EPC ties supporting two rails inside a ballast box, with two hydraulic actuators simulating railroad bogie loading for over 350,000 cycles per actuator. Track displacement, flexural and shear strains, and distributed fiber optic measurements were used to characterize the structural response, supplemented by analytical evaluation and temperature correlation analysis. Small-scale fatigue testing demonstrated relatively stable flexural stiffness, with apparent stiffness-based damage remaining below 1% and partial stiffness recovery observed during cyclic loading. The full-scale experiment revealed differential track settlement and nonuniform flexural and shear strain responses, while analytical and experimental results highlighted the importance of localized shear deformation near the rail seats. Strong correlations were also observed between outdoor air temperature and daily mean recorded strains, although potential gauge-related effects could not be independently quantified. Post-fatigue mechanical testing showed average reductions of 6.35% in modulus of elasticity and 33.14% in modulus of rupture relative to separate unfatigued specimens. Forensic examination further revealed substantial manufacturing defects in a tie that fractured during the early stages of testing. Overall, the findings demonstrate the importance of considering localized flexural and shear strain response, track support conditions, and manufacturing quality alongside conventional mechanical characterization when evaluating the fatigue performance of EPC railroad ties.