| With the relevant technology of high speed EMU becoming mature,railway transportation in our country is developing rapidly.There is a lot of welded structures in car body and key bearing part of EMU,and welded structure fatigue strength decides the structure design is safe and reliable or not.Based on the importance of welded structure fatigue performance,developing a set of welded structure fatigue strength assessment method which is suitable for our country condition,that is the inevitable demand of industry development.At present,in the locomotive design field of railway industry,nominal stress method is used to assess the welded structure fatigue structure fatigue strength mostly.But differences between standards obviously,which make locomotive designers in convenience.In order to solve this problem,the paper aims at BS standard,IIW standard and JIS standard which belong to nominal stress method,to study and make comparative analysis;Second,Make the nominal stress method and the hot spot stress method which are in the IIW standard to compare with the master S-N curve method of the ASME standard,to study their advantages,disadvantages and application strategy;thirdly,in view of the factors which influents the welded structure fatigue strength,such as welding residual stress,thickness and improved process after welding,making them compare with each other.Finally,according to the above content analysis results,this paper chooses a high speed EMU trailer bogie as analysis object,and uses the master S-N curve to access the positions which is liable to fatigue damage in the project.In this paper,through the study of the content above.and contacting the common fatigue problems of railway industry,makes the conclusion that the S-N curve which is suitable for assessing the fatigue strength of welded structure in high speed EMU,which should select stress range as stress analysis parameter,and the fatigue test results of welded joints with high cycles as the scope of design life,and also should take the influence of survival rate which recommended is 97.7%into consideration.When the nominal stress method is used to assess the welded structure fatigue strength,it will not be affected by element size,but can't reflect the impact of local geometric change.Hot spot stress method and master S-N curve method can reflect the influence by local detail changing to the welded structure fatigue strength,but the element size influent the calculation accuracy of hot spot stress method obviously,but master S-N curve method can solve the problem well.Using a coefficient to correct the S-N curve,in order to reflect the influence of residual stress to welded structure fatigue strength,and it's better to be similar to IIW standard which gives detailed classification;it is recommended that using,the thickness correction method which is given by BS standard and master S-N curve method to reflect the influence by the thickness to welded structure fatigue strength;it should be clear that the effect of all kinds of improved process after welding to welded structure fatigue strength,and it's better to make it as a safety margin of welded structure fatigue strength,not to take it into consideration in the design phase.By comparing the results,there is no need for master S-N curve to distinguish the concrete form of welded joints.In addition,Master S-N curve can reflect the local geometric changes,and its element sensitivity can guarantee good calculation accuracy.So it is suitable to assess welded structure fatigue strength.Finally,the result of the analysis shows that the fatigue strength of the bogie meets the design requirements,and fatigue damage of the anti-side-rolling torsion pole is large when the bogie is working.According to the equivalent structure stress curve by calculation,it can help the designer to analysis and improve the structure effectively. |
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