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

Abstract

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.

The microstructure, mechanical, and fatigue behaviours of MAG welded G20Mn5 cast steel

“…Therefore, it is the crack nucleation that controls the fatigue lifetime. FCG rate is a significant fatigue resistance index for both the structural design and service maintenance of critical structures, such as railway axles, bogie frames, and brake discs . Figure gives the FCG curves of the G20Mn5 matrix and welded joints.…”

“…FCG rate is a significant fatigue resistance index for both the structural design and service maintenance of critical structures, such as railway axles, bogie frames, and brake discs. 21,35,64,65 Figure 13 gives the FCG curves of the G20Mn5 matrix and welded joints. The calculated threshold stress intensity factor (SIF) ΔK th for the matrix (9.96 MPaÁm 1/2 ) is much larger than that of the MAG welded joints (4.42 MPaÁm 1/2 ).…”

“…With the increased popularity of China high‐speed railway in the past few years, the operating conditions of railway vehicles have become more stringent . As a safety critical structure of railway vehicles, the bogie frames with stabilizing devices are responsible for the smooth running and operation of the vehicles . Furthermore, the combined effects of vibration and cyclic loadings greatly limit the service performance .…”

“…Even so, the 25‐year life or more of bogie frames in operation must be ensured . As a classical joining technology, metal active gas (MAG) arc welding can efficiently manufacture the modern railway components . Unfortunately, systematic investigations on the fatigue crack resistance of MAG welded G20Mn5 cast steel are still lacking.…”

“…[24][25][26][27] As a classical joining technology, metal active gas (MAG) arc welding can efficiently manufacture the modern railway components. 13,21,[28][29][30][31] Unfortunately, systematic investigations on the fatigue…”