PSI - Issue 22

C.L. Niu et al. / Procedia Structural Integrity 22 (2019) 361–368

364

4

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



 h 1/ 

ess k d N S C , /  

（ 4 ）

When considering welding defects,       N a t a t n i     / 1 / 0 /

m

C M K C td a t m  1

    I r t m    2 1

（ 5 ）

s

kn

n

In formula 5, a is the initial crack length, t is the thickness of plate, N is the fatigue life value, n and m are constant, kn M is the stress intensity amplification factor caused by weld toe notch, ( ) I r is the dimensionless function of load bending ratio r, K  is the range of stress intensity factor change. 5 ） The fatigue damage of the k th cycle is calculated and the number of cycles of the k th cycle is set to k n . N D n  , 6 ） Repeat steps 3 to 5 for all stress ranges. 7 ） Calculate cumulative damage. If the evaluation position of the welded joint meets the following conditions, continue the next step.     M i f k f D D 1 , 1.0 8 ） Repeat steps 3 to 7 for each location of the welded joint to complete the fatigue life assessment. 9 ） The equivalent structural stress ess k S ,  is calculated according to the structural stress obtained in the calculation, and then the life N calculated from the master S-N curve is compared with the design life ref N to verify whether it meets the life requirement, and the equivalent structural stress ref S  under the design life is calculated by the calculation formula (6). h ref d ref S C N    （ 6 ） 10 ） The actual equivalent structural stress ess k S ,  is compared with the design value ref S  to calculate the stress factor, such as formula (7). Stress factor = ref ess k S S   / , （ 7 ） Defects are inevitably introduced in the welding process. Fatigue assessment of welded structures with defects can be carried out by the equivalent initial crack method in ASME [11-12]. 11 ） According to the obtained stress factor value, the corresponding stress state grade is determined according to EN15085-3 principle. The evaluation process based on structural stress method is programmed by C language. The calculation results are saved with the output of .xls file. 3. Engineering Application of Stress State Grade Assessment Method Because of the large number of welded joints and the complexity of the types, the validation of the evaluation method is carried out on the H-type welded frame of a freight car. 3.1 Welded Frame model and Load The finite element model of the frame with welded joints is established in HyperMesh with hexahedron solid element. The total number of model elements is 1091298 and the total number of nodes is 1393811, including the finite element modeling of the main structure of the welded frame and its accessory mounting seat structure. In order to ensure the consistency with the support position of the test outline, spring elements are established in the performance simulation model to constrain the vertical support frame; the lateral and longitudinal supports are usually connected with the swivel boom by the RBE2 and RBE3 elements in HyperMesh software. The main k k f k