A time-domain stepwise fatigue assessment to bridge small-scale fracture mechanics with large-scale system dynamics for high-speed maglev lightweight bogies

•A new time-domain stepwise fatigue assessment is proposed to successfully tackle structural integrity problem of maglev bogies.•Small-scale fracture mechanics based damage tolerance are well bridged with large-scale vehicle system dynamics.•Fatigue life of defective components correlate with routes and suspension parameters.•When initial crack length is 3 mm, remaining life of swing bar of high-speed maglev lightweight bogies is reduced significantly. Maglev trains with an operation speed higher than 600 km/h show a great advantage during the next generation ground transportation. To tackle the structural integrity of maglev bogies made of forged 6082-T6 aluminum alloys, a time-domain stepwise fatigue assessment (TSFA) approach was proposed to consider complex dynamic fatigue loads. Firstly, a vehicle-bridge coupled maglev vehicle dynamic model was established to obtain the time history of service-simulation fatigue loads. Secondly, these variable-amplitude fatigue spectra were introduced to examine the damage accumulation lifetime of the maglev bogie using classical nominal stress method, the swing bar of high-speed maglev bogies was then identified as the safety critical component. To further enhance the service safety and reliability, the remaining life of the swing bar was investigated using damage tolerance method in terms of a real fatigue failure accident from Shanghai maglev trains. Calculation results indicate that the remaining life is sharply reduced from 34.1 years to 19.7 years when an initial crack length of 3.0 mm is generated at the swing bar. More conservative but practical fatigue life can be acquired when using the new TSFA framework instead of individual damage tolerance or safe-life method.