13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- . 1 3 2 ρ ρ ρ m m K + + = (42) If the crack height h tends to zero, one has 0, =m 1=ρ and then Eq. (41) reduces to 2 1. 1 3 K m m ρ ρ ρ = = + + (43) which is the solution of Griffith cracks in a 1D hexagonal QC [15]. 4. Numerical examples We consider the variation of K with h a β= . It can be shown from Fig. 3 that if 1 β< , the dimensionless field intensity factor K decreases with the value of β becomes large. It indicates that an increase of the height of the tip-shape crack will retard the crack propagation. In particular, when the height of the lip-shape crack approaches to zero, the current case can be reduced to the Griffith crack, i.e., 1 K= , which is easier to propagate. Figure 3. Variation of Kwith h a β= Acknowledgements The authors thank the support from the National Natural Science Foundation of China (Nos.11262012 and 11262017), the Scientific Research Key Program of Inner Mongolia University of Technology (Grant No. ZD201219). References [1] D. Shechtman, I. Blech, D. Gratias, J.W. Cahn, Metallic phase with long-range orientational
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