Analysis of the dynamic response and fatigue reliability of a full-scale carbody of a high-speed train

Abstract

For a vehicle operating under different line conditions, coupled with track irregularity and many other factors, the carbody is subjected to extremely complex random loads, and the load mainly exists in the form of an alternating load; therefore, the primary type of failure is fatigue failure. With the continuous improvement in train speed, lightweight designs of carbody structures and the application of high-strength aluminium alloy, the safety and reliability of a carbody require more attention. An investigation of the dynamic fatigue reliability of a full-scale carbody of a high-speed train under random load conditions is carried out. A dynamics model of the vehicle system has been established for acquiring the time history of forces acting on the carbody by each air spring (hereinafter referred to as 'the load-time history'). A surrogate model (a simple model instead of a complex carbody model) of the carbody is established based on the Box-Behnken matrix design and the polynomial fitting method; then, the load-time history is transformed to the stress-time history of the points of concern, and the results are compared with the results of the transient analysis, which verify the accuracy and effectiveness of the surrogate model. Then, a stress block spectrum is obtained by rain flow counting, and the stress probability distribution is determined. Combined with the probability distribution of fatigue strength, a dynamic stress-strength interference model (the area of interference between strength and stress in the model changes over time) is established. The failure rate and dynamic reliability of the points of concern for two cases are analysed: without considering the strength degradation and considering the strength degradation. The results show that without considering the strength degradation during service, with increased service mileage, the fatigue strength reliability of the points of concern decreases continuously, and the corresponding failure rate of the points of concern decreases with time and reaches a steady value, which has the characteristics of the first two stages of the bathtub curve. By considering the strength degradation during service, the reliability of the points of concern decreases gradually, and the corresponding failure rate of the points of concern decreases and then increases, with all the features of the bathtub curve. In addition, compared with the base metal region, the fatigue resistance of the welded structure decreases due to welding. Under the same service conditions, the reliability of the welded region is relatively low, and fatigue failure is more likely to occur.

Analysis methods of the dynamic structural stress in a full-scale welded carbody for high-speed trains

“…Although the calculated results are still insensitive to the mesh, the geometric stress concentration effect is not included in the results, so the structural stress is closer to the nominal stress. Since the structural stress method is used to predict the fatigue life of carbody, it is necessary to modify the calculated structural stress by multiplying the correction factor (see equation (13)); otherwise, the calculated structural stress results are unsafe…”

“…Multidisciplinary methods integrate application of the vehicle system dynamics method, the finite element method, the polynomial fitting method, and so on. Lu et al 13 used multidisciplinary methods to obtain the nominal stress of the carbody and analyzed the dynamic reliability of the carbody. Wu et al 14 used the shell element and the beam element to perform finite element analysis, obtained the stress-time history of boom girders of a concrete pump truck, and compared it with the stress-time history obtained from the lab test to verify the accuracy of results.…”

Sensitivity analysis for operating loads in fatigue design of railway vehicles

“…6,7 Applying these loads to the car body structure, the fatigue life can be evaluated for different design solutions 8 and a reliable analysis can be performed. 9 For the virtual fatigue design a probabilistic modelling approach, considering uncertainties in the load and vehicle parameters is implemented in this project. Applications of such modelling approaches can be found for component design e.g.…”

“…6,7 Applying these loads to the car body structure, the fatigue life can be evaluated for different design solutions 8 and a reliable analysis can be performed. 9…”

Analysis of the aerodynamic pressure effect on the fatigue strength of the carbody of high-speed trains passing by each other in a tunnel

“…[16][17][18] The fatigue life of the carbody is predicted by the accumulated damage method. [19][20][21] The traditional design generally does not consider the influence of aerodynamic load. However, fatigue assessments that ignore aerodynamic loads cannot accurately and objectively describe the influence of pressure waves on the strength of the carbody.…”