Fracture mechanics based residual life prediction of railway heavy coupler with measured load spectrum

To assess the residual life of railway truck heavy couplers made of cast steel with initial defects, a testing campaign has been carried out to determine high cycle fatigue strength, fatigue crack growth rate, threshold, and fracture toughness. The numerical model of a damaged No. 17 heavy-haul coupler is established, by fully considering the assembly clearance and the complex nonlinear contact. The fracture mechanics based remaining life under the actual load spectrum is then found. The results show that the remaining life with an initial 4-mm-length surface crack inside the heavy coupler are about 704,300 km and 761,800 km when using the classical Paris law and the advanced NASGRO equation respectively. Based on the advanced NASGRO equation, approximately 12.8% of the life is retained when there is a 20-mm-length crack. The maximum load-carrying capacity of the cast steel couplers shows an exponential downward trend with increases in crack length. The critical size for a non-propagating crack can be assumed to be 20 mm after considering possible high impact loads in service. The predicted mileage is 664,100 km, i.e., the life is about 3.32 years, which is larger than the inspection interval currently used for a railway truck heavy coupler.