| The bolster is a significant load-bearing component of the train vehicle.During bolster service,it will experience cumulative damage by the loads,which is a potential threat to the safe service of the train and the personal safety of the passengers.The bolster is a large and complex box structure,and is welded by aluminum alloy sheets and profiles.There are hundreds of welds in it,and the stress concentration zones,namely weak points,are usually located at the weld sites.It is challenging to find fatigue cracks on the bolster in time due to the lack of an effective method to monitor the state of weak points in real time.There is an urgency to provide robust methods to assess the fatigue life and reliability of the bolster.The method presented in this paper builds on our detailed studies in the metro-train bolsters and the high-speed train bolsters.The following findings are demonstrated in this paper:(1)The fatigue life of a metro-train bolster in the test environment was evaluated using the fatigue test and theoretical calculation.Meanwhile,a fatigue load equivalent method,which reduces the fatigue test cost without affecting the test results,was proposed.According to the international standards and the finite element analysis results of the metro-train vehicle,the fatigue test procedures of the bolster were determined and the fatigue test platform was established to study the fatigue life of this metro-train bolster in the ambient environment.Since the bolster was modeled as a series system of the weak points,which means that the fatigue life of the bolster is the shortest life among the weak points',its fatigue life was assessed using the finite element method(FEM)and the Gerber diagram.(2)The corrosion-fatigue life of the high-speed train bolster was studied considering the influence of corrosion environment on the fatigue life of the bolster.Based on the accelerated-corrosion environment spectrum and fatigue test procedures,the corrosion-fatigue test platform for the high-speed train bolster was established.According to the established corrosion-fatigue test method,the fatigue life of the bolster in an acidic corrosion environment was studied.Meanwhile,the corrosion-fatigue life of the bolster was assessed using the FEM calculation and the Gerber diagram in combination with the corrosion-fatigue properties of the fillet weld.(3)Considering the effects of many factors,including load uncertainty,material properties uncertainty,load application times and material strength degradation,on fatigue life and reliability of the weak points,a weak point selection method for complex structures with multi-variable reliability model was proposed.Meanwhile,a virtual experimental method,in which the real fatigue tests are replaced with the computer simulations,was proposed.The fatigue life and reliability of the metro-train bolster was then assessed with these methods,which greatly reduced the evaluation time and cost.(4)Using the theoretical calculation and fracture analysis,including macroscopic analysis,chemical composition analysis,and microscopic analysis,the crack source and causes of a corrosion-fatigue crack on a high-speed train bolster were clarified.The crack propagation rate was determined by micro quantitative analysis,the relationship between the crack propagation rate and the crack length was obtained by the FEM simulation,and the crack propagation life was finally calculated to assess the service-safety of the bolster.(5)Based on the dissimilar-dimension interference model,a model for evaluating the fatigue reliability of complex structure under random loads was proposed.This model not only simplifies the complex structure by regarding multiple weak points as a series system with multiple units,each containing only one weak point,but also takes into account the statistical correlation of fatigue failure of the weak points due to the load uncertainty.This model was used to assess the fatigue reliability of both the high-speed train bolster and the metro-train bolster. |
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