13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Three-dimensional lap joint specimen model is created as shown in Fig.12. The full scale joint is modeled considering the features of material nonlinearity, out-of-plane bending, pin-load and friction contact. Both the pieces and rivets are meshed by 10 nodes tetrahedron solid element SOLID92. All the possible contact areas are modeled, and the rivets are modeled as ‘neat fit’ to holes and plates. The surface of model has the same displacement restriction as the specimen for the best boundary condition approximation. Figure 12. Finite element model of lap joint specimen Figure 13. Von Mises stress of piece1 Three-DOF constrain was applied on one side of the model, and pulling stress (120MPa) was evenly applied on the other side. Fig.13 shows the stress distribution of piece 1. The maximum stress concentration of lap joint locates on the right hole’s edge of the first rivets row, it shows an excellent accordance with the crack initiation locations observed in tests. The maximum stress is 385MPa and the maximum strain is 0.0068 when the pulling stress is 120MPa; the maximum stress is 59.8MPa and the maximum strain is 0.00088 when the pulling stress is 7.2MPa. 4. Fatigue life estimate In order to verify the validity of simulation method and establish links between FEA and test, fatigue lives of two different joints were estimated. 4.1 Fatigue life estimate of FSW joint The fatigue life of FSW joint is estimated according to residual stress result and base metal S-N curve [9] on the bridge of Goodman formula. We have known that the maximum residual stress of FSW joint is 115MPa. When the FSW joint under the constant amplitude load spectrum which maximum stress is 180MPa and stress ratio is 0.06 (accord to Fig.7, the fatigue life is 224566), the maximum local stress of joint is 295MPa ( max ' 180+115 ) and the stress ratio is 0.42 ( 180 0.06+115 ' 180+115 R ).
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