Research On The Fatigue Strength Of Welded Aluminium Alloy Vehicle Body Based On ASME Standard

With the rapid development of the railway toward high speed and heavy load in China, it demands for higher quality of the vehicle structural performance. The vehicle body is not only the supporting frame of the whole vehicle, but also the basement for other equipment. One of the most important indexes for welded structure reliability design is the fatigue life. Under alternating or random loads, fatigue failure of the structure mainly begins from the welds, which have direct effects on safe operation of the vehicle.The prediction of the weld fatigue life is always a difficult problem worldwide. As for the common used method nowadays, nominal stress method of weld structure is the commonly used way nowdays, which is easy to use but has its limit from the geometry of weld joint, welding defects and loading status, for complex welded joints it has the limitation to use. The equivalent structural stress method is a new fatigue life prediction method invented by Chinese-American scholar P.Dong. This method is based on fracture mechanics principles and plenty of welding fatigue test. It takes the element size-insensitive structure stress and one main S-N curve to calculate the fatigue life of weld structures, which largely improves the prediction accuracy.ANSYS produces large amounts of data after calculating, the data is stored in the result file. It is necessary to obtain the stress distribution under different loading status in structure fatigue analysis or life prediction. But the efficiency is low to access the data by hand according to finite element method. Thus this paper firstly analysis the formation of ANSYS RST binary file, then reads the data in the result file by a program written in FORTRAN to obtain the data of what we need in fatigue analysis, which can reduce the time of post processing and improve the efficiency.This paper use shell element to bulid the FE model of an urban rail vehicle aluminum alloy body. The load cases of static strength and fatigue strength analysis are based on EN12663-1 and then evaluate the static strength according to von Mises stress. After meeting the static strength requirements, write weld fatigue analysis program in FORTRAN based on the equivalent structural stress method of ASME standard, then combine with the main S-N curve to predict fatigue life of the important welds on the vehicle body.