Fatigue-related internal cracking in rail heads remains one of the primary threats to heavy-haul railway safety and reliability. Subsurface cracks can grow undetected under repeated wheel–rail loading, eventually leading to rail fracture, service interruptions, and costly maintenance interventions. To improve predictive capabilities and inspection strategies, reliable experimental data are required to calibrate physics-based fracture models.
This project, conducted at Texas A&M University, investigates a simplified and scalable methodology for characterizing fatigue crack growth in pearlitic rail steel. A retired rail segment containing a natural internal flaw was waterjet-cut and machined into a prismatic specimen, positioning the crack at the center of the gauge section. The specimen is subjected to controlled tension–tension fatigue loading while crack evolution is monitored using Phased Array Ultrasonic Testing (PAUT).
Unlike prior full-scale multiaxial railhead bending tests—which replicate in-track loading but require complex fixtures and higher experimental costs—this uniaxial configuration isolates Mode I (tensile-dominated) crack propagation under controlled boundary conditions. The objective is to extract core fracture properties that can be used to calibrate cohesive-zone and multiscale computational fracture models developed within CRR research efforts.
Key Outcomes to Date
- Successful detection and monitoring of internal crack growth using PAUT during cyclic loading.
- Measurable crack evolution beyond one million load cycles.
- Identification of early-stage variability due to ultrasonic coupling sensitivity and grain-scale crack arrest.
- Demonstration that simplified uniaxial fatigue testing can provide repeatable, high-quality fracture data at reduced cost and complexity.
Although uniaxial loading does not replicate the full multiaxial stress state experienced in service, it serves as a material-level constitutive test for identifying fracture parameters. These parameters will be integrated into validated multiaxial rail models to improve crack-growth prediction and life assessment of heavy-haul rails.
Ongoing and Future Work
Current testing continues toward complete fracture to capture late-stage crack acceleration and final failure modes. Planned post-mortem analyses include SEM and EBSD characterization to quantify microstructural influences on crack propagation. Advanced ultrasonic modalities, including Full Matrix Capture (FMC) and Time-of-Flight Diffraction (TOFD), will be evaluated to enhance subsurface defect resolution.
This research supports CRR’s mission of advancing rail integrity assessment through experimentally validated, physics-based modeling and nondestructive evaluation techniques, ultimately contributing to safer and more resilient rail infrastructure systems.