Research on size effects in fracture properties and residual life prediction for high-speed train axles

As critical load-bearing components of high-speed trains, the design and evaluation of axles primarily adhere to the principle of infinite life, supplemented by systematic flaw detection to ensure their operational safety. The establishment of detection intervals heavily depends on damage tolerance analysis informed by fracture mechanics. The size effect has a great influence on the fracture mechanical properties of materials, and how to accurately assess the remaining life considering the dimensional effects has been an open question in terms of safety in the railroad industry. Consequently, this research focuses on full-scale axle crack propagation tests, exploring the fracture mechanics properties critical to the life analysis of full-scale axle cracks under very high cycle fatigue (VHCF) condition. The findings demonstrate that size effects profoundly affect the fatigue fracture properties of high-speed train axles, especially regarding fatigue crack growth thresholds. Importantly, within the stable growth region, variations in fatigue crack growth rates across different scales prove to be minimal. Subsequently, a finite element model of the full-scale axle was established using the fatigue crack growth rate curve derived from experimental data. The validity of this FEA model was confirmed through bench test results, and predictions of the residual life for axles with cracks were formulated. This comprehensive analysis provides the foundation for developing an ultrasonic detection interval schedule for axles.