PSI - Issue 22

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

358

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

4.3 Rapid screening of weak fatigue sites Applying the program compiled in this paper based on IIW-2008 and DVS1608-2011 standards to evaluate the stress state grade of welded joints of aluminium alloy vehicle body, it is found that the calculation speed is very slow and the evaluation period is very long because there are a lot of welds in different forms and directions in this EMU body. In order to improve the calculation efficiency, save time and computer resources, by introducing the HyperView module with visualization function to filter the whole welds, the typical weld area of the vehicle body can be quickly determined. The specific screening process is as follows: 1) The finite element model of vehicle body under fatigue load is simulated by ANSYS, and the analysis results are obtained; 2) Using the Derived Load Steps command in HyperView, select the Linear-Superposition command in Type, and randomly select the calculation results of any two working conditions in the fatigue load condition to perform linear superposition (vector difference); 3) Using the Derived Load Steps command, the Envelope command and Extreme command are selected in Type, and the calculation results of all superposition working conditions are combined to form the calculation results of "Envelope-Extreme working condition", because the absolute value of the maximum principal stress of "Envelope Extreme working condition" is larger than the variation range value of the principal stress based on the standard stipulation. Therefore, the absolute value of the maximum principal stress of the "Envelope-Extreme condition" can be displayed through the visualization window, and the typical welds in the fatigue weak parts of the vehicle body structure can be quickly determined, and then these typical welds can be evaluated according to the evaluation criteria. Under the condition of fatigue load, the Section4.3 rapid screening method was used to determine the main bearing areas of the weak parts of the vehicle body fatigue in the area of side wall door and column, the connection area between floor side beam and equipment cabin and diagonal partition wall, the profiles of floor and traction beam, and the vicinity of roof air conditioning frame. There are seven typical welds in this area: weld 1 is the longitudinal weld between the side beam and the floor on the upper surface, weld 2 is the weld between skirt plate and side beam, weld 3 is the weld between partition wall and aluminium floor of equipment cabin, weld 4 is the lateral weld between side wall door column and side wall, weld 5 is the internal weld between side wall door column and side wall, weld 6 is the longitudinal weld between side beam and side wall and weld 7 is a weld near the roof air conditioning frame. By using the IIW-2008 standard evaluation procedure of Section3.2, the principal stress vector directions of these typical welds can be obtained (the principal stress vector diagrams of some welds are shown in Figure.4), and the FAT level can be determined by the principal stress vector directions and the types of welded joints. The evaluation results of these typical weld stress state levels are shown in Table2, the table shows the calculated stress variation amplitude, FAT level and corresponding allowable stress variation amplitude of the welded joints. It can be seen from Table2 that the longitudinal weld between the side beam and the side wall has the largest stress factor, the value is 0.811, and the stress state level is medium; the rest of the welds have low stress state levels. 4.4 Evaluation of stress state level

(a) weld 1

(b) weld 2

(c) weld 3

(d) weld 6

Fig.4. The principal stress vector diagram of partial typical welds