13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- fracture occurred when the fracture propagation reached 3/4 of sample width. The fracture also occurred at impact zones at same time. Fig. 7 Effective strain rate distribution in DWTT samples (s-1) The appearance of the simulated fracture surface is in close agreement with the experimental results [18] in terms of stress distribution and fracture morphology as shown in Fig.8. Fracture was initiated as cleavage fracture followed by shear fracture, and then an inverse fracture occurred at the impact zone of the sample. Further analyses on ductile-brittle transition will be carried out by developing a coupled brittle/ductile fracture model in the near future. The relationship between the initiation of inverse fracture and the length of mixed fracture zone need to be further investigated. Fig. 8 Simulated results versus the experimental results obtained in ref 18. 4. Conclusions (1) A finite element model using the Gurson-Tvergaard-Needleman damage model was employed to simulate the fracture process of pipeline steel during DWTT, in particular, considering the state of initial stress around the pressed notch. (2) During DWTT, the fracture follows a triangular shape in the sample due to higher constraint at
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