Study On Fatigue Life Forecasting Of EMU Car Body Including Welding Defects

Aluminum alloy has the properities of high strength, low density, non-magnetic, good corrosion resistance and formability, so it is widely used in high-speed EMU manufacturing field. However, in the process of welding, aluminum alloy welded joints may appear some welding defects, such as undercut, incomplete fusion, porosity, imperfect penetration and inclusions. If the number of these defects are more enough or the size are large, it would significantly reduce the fatigue life of aluminum alloy car body. However, so far there is lack of assessment criteria about the different welding defects affect the fatigue life of EMU car body, so it has the great significance to obtain the law of different welding defects affect the fatigue life of EMU car body, through the method of combine experiment and simulation.The main contents are as follows:⑴ In order to understand the law of welding defects affect the fatigue properities of aluminum alloy specimen, respectiely do fatigue test of 6082 aluminium alloy welded specimen with the defects of undercut and porosity, obtained fatigue test data of the relationship of stress amplitude and cycle times; According to the fatigue test results, drew the S ?N curves of specimens; Based on structural stress method worked out the "equivalent initial crack" of aluminium alloy welded joint which with undercut and porosity defects.⑵ Established finite element model of certain type domestic EMU middle car body, reference to BS EN12663-2010 standard, analyzed the strength and rigidity of model’s 12 kinds of load conditions. Based on structural stress method, nominal stress method and Miner linear fatigue damage cumulative theory, predicted fatigue life of the car body risk welding line;⑶ Reference to the new S ?N curves, based on the IIW standard to predict the fatigue life of car body with welding defects; Applied the theoretical numerical value of equivalent initial crack to car body analysis, then predicted fatigue life of EMU car body with welding defects by structural stress method;Through fatigue test, obtained S ?N curves of specimens with undercut and porosity defects; Based on structural stress method worked out "equivalent initial crack"; Based on nominal stress method and the structural stress method to carry out the research on welding defects affect fatigue life of aluminum alloy car body.The results show that: the existence of welding defects have a significant adverse effect on the fatigue life of EMU car body.