13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- respectively. It is to be noted that the deformation is magnified by 100 times to reveal the details of the interface crack. Obvious crack open displacement and stress concentration can be found around the crack tip. Moreover, the difference in the normal stress acting where before and after the crack tip the obstructing effects of the interface crack on the propagation of the tensile stress pulse. Fig. 5 Magnified contour of stress component SY at the time point t=1.03μs Fig. 6 Magnified contour of stress component SXY at the time point t=1.03μs The crack open displacement at the node 5μm away from the crack tip is further shown in Fig. 7. It is verified again that the crack is always open after the compressive pulse transmits across the interface crack, although some slight fluctuation arises due to the quick reciprocating of the film under impacting. Fig. 7 Crack open displacement at the inner node 5μm away from the crack tip The peak values of normalized dynamic strain energy release rate [4] (DSERR) versus crack length are shown in Fig. 8 for the model under the three initial stress states, in which the time value in bracket denote the time point when the peak value arises. One can see that the maximum DSERR appears when the crack length if about 65 percent of the impact region radius. One can also see that the peak value of DSERR almost all appears around the time point t=1μs if the crack length is less than 75 percent of the impact region radius, while the time when peak value arises will be
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