Damage Tolerance Assessment of a Brake Unit Bracket for High-Speed Railway Welded Bogie Frames

The brake unit bracket of a bogie frame is an important load-carrying component,particularly under emergency start/stop conditions.Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime,which hinders the lightweight design of modern railway vehicles.In this study,to ensure the reliability and durability of a brake unit bracket,an attempt was made to integrate the nominal stress method and an advanced damage tolerance method.First,a complex bogie frame was modelled using solid elements instead of plate and beam elements.A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan-Guangzhou high-speed railway line.Based on the probability of foreign damage,a semi-elliptical surface crack was then assumed for residual life assessment.The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years.Moreover,even if a 2-mm depth crack exists,the brake unit bracket can be safely operated for more than 2.27 years,with the hope that the crack can be detected in subsequent maintenance procedures.Finally,an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.