PSI - Issue 22

S.M. Xie et al. / Procedia Structural Integrity 22 (2019) 353–360

354

2

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction The lightweight EMU body uses a large number of hollow extruded aluminum alloy profiles, which are welded together to form a vehicle body structure, and the welded joints and weld forms are diversified, decentralized and complicated, which leads to the decrease of the strength, stiffness and fatigue life of the body structure. Therefore, the anti-fatigue design of the welded joints of the aluminum alloy EMU body has become a key issue of increasing concern. At present, the research on fatigue strength of aluminum alloy vehicle body of EMU mainly focuses on the prediction of fatigue life and bench test of vehicle body. K. Liu used IIW standard based on nominal stress method to analyze the fatigue of the weld of CRH3 high speed aluminum alloy EMU body, and used linear cumulative damage theory to evaluate the fatigue damage and life of the weld [1] ; Y. Song studied the fatigue test method of aluminum alloy EMU body, including constant and variable amplitude loading test and aerodynamic load fatigue test on the vehicle body, evaluated the fatigue life of the vehicle body [2] ； S.M. Xie, etc based on structural stress, the stress distribution characteristics of welded joints of aluminum alloy EMU body were studied, and the fatigue strength of vehicle body weld can be improved by grinding and other improvement technologies in areas needing attention [3] . The welding standard for the design of welded joints of aluminum alloy EMU body is BS EN15085-3, which stipulates that the stress state level of welded joints is determined by the stress factor [4] . At present, the fatigue design of welded joints for aluminum alloy vehicle body designers has also begun to pay attention to the stress level of welded joints. On the basis of studying the fatigue assessment methods in DVS1608-2011 and IIW-2008, this paper takes an aluminum alloy EMU body as the research object, and uses these two standards to study the stress state level of the welded joints of the vehicle body on the premise of meeting the fatigue life requirements [5 - 6] . 2. Stress state level assessment method based on DVS1608 standard This standard is applicable to the fatigue strength evaluation of extruded profiles, plates and forged base metals and arc welded structures of aluminum alloys EN AW-6005A and EN AW-6082 in rail vehicle manufacturing. It meets the requirements of BS EN15085 standard for welding structure. 2.1 Nominal stress assessment method The steps for evaluating the stress status of welded joints by the nominal stress assessment method in DVS1608 2011 are as follows: 1) The finite element model with welded joints under fatigue loading is simulated and calculated to determine and evaluate the weld and establish the local coordinate system of the weld; 2) The normal stress parallel to the weld //  , perpendicular to the weld   and shear stress along the weld direction //  are extracted from all working conditions in the local coordinate system of the weld. The next step is to find the directional stress extremes of the evaluation points   // max  ,   max   ,   // max  ,   // min  ,   min   and   // min  , and calculate their respective stress ratios //  R ,   R , //  R and stress amplitudes   a //  ,   a   ,   a //  ; 3) The allowable fatigue strength of aluminum alloy welded joints is only related to the stress ratio  R and  R . Firstly, the number of weld notch curves x is determined by the form and load-bearing condition of welded joints, and then the allowable fatigue strength amplitude of welded joints is calculated according to the formula of the corresponding fatigue strength amplitude of stress ratios in different ranges. 4) Calculate the bearing capacity x a , y a and  a in one direction







      a

    //  a

  a

(1)

//

//



x a 

y a

 a 



；

；







  // 

a zul R

a zul R

a zul R

     a zul R and

  //   a zul R ,

  //   a zul R are the allowable fatigue strength amplitudes corresponding to the three

Among them:

directions. If the structure is in a multiaxial stress state, its bearing capacity is v a (where v f takes 1)

(2)

    2

      2 //  f a a a v   

2

a a a 

  

//

v

