Study On Fatigue Damage And Life Prediction Based On Dynamic Response Frequency For Double-Spot Welded Joints

In this paper, fatigue damage process of double-spot welded joint was studied by FEA and fatigue testing. The mechanism of cracks initiation and propagation was studied in several aspects. The characteristics of natural frequency were investigated based on the simulation by 3D finite element analysis and the dynamic response experiments for spot-welded specimens during the fatigue damage process. The results of the simulations showed that a good agreement was achieved with experimental analysis. 3D finite element simulation can reflect the changes of natural frequency for double-spot welded joints during the fatigue damage process. Mode shapes for double-spot welded specimen were calculated by FEA software, and the reason that all modes natural frequencies decrease in different extent was discussed. In addition, this paper discussed the relationship between the natural frequency relative changes and the fatigue damage for double-spot welded joints during the fatigue process. The results showed that the relative changes of natural frequency are independent of the dimensions of specimens. Based on the fatigue experiment and FEA simulation, the fatigue damage and fatigue life were predicted for double-spot welded specimen.First, the crack initiation and propagation were discussed in the below four aspects: loading state,material ingredient,rigidity,crack shape. A series of fatigue tests were carried out on MTS810 material test system for spot-welded specimens, combined with the dynamic response experiment, the characteristics of natural frequency were obtained during the fatigue damage process.Then, the FE model was constructed according to the specimen dimensions and the rule of crack initiation and propagation. The fatigue damage process and the characteristics of natural frequency of spot-welded specimens were simulated by 3D finite element analysis. The results of the simulations showed that a good agreement was achieved with experimental data.Finally, on the basis of the finite element analysis and experiment results, the fatigue damage and fatigue life of double-spot welded specimen was estimated. The results of prediction showed that a good agreement was demonstrated with experimental data.