13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Figure 2). This awkward phenomenon results form the cut-off function in the Erhart-Albe (Tersoff-like) potential [27]. The results from SW and MEAM potentials are much lower than the ab initio calculations. Therefore, we select the EDIP model for the following calculations. Figure 2 Strain-Stress relations of bulk silicene under tensile tests in the zigzag and armchair directions with different potential. Table 1 Young’s moduli for bulk silicene from ab initio calculations and different potential models. All values are in units of GPa. Direction of tension Ab initio results EDIP Erhart-ALbe SW MEAM Zigzag direction 148.5 166.7 120.7 73.3 57.2 Armchair direction 140.7 170.8 121.2 67.0 56.1 Figure 3 Evolutions of bond length (a) and bond angle (b) with a function of strain when uniaxial tension is applied on bulk silicene along zigzag and armchair directions. As the strain increases, the chirality dependence becomes obvious for all potentials. As for EDIP model, the critical strain is 15.5% and 19.5% in the armchair and zigzag direction, respectively. The calculated critical stress of bulk silicene is 15.5 and 18.1 GPa in the armchair and zigzag direction, respectively. The critical strain and stress are different for zigzag and armchair load tests. To give more insight into this phenomenon, the variation of the bond length and bong angle with the strain in the tensile direction for zigzag and armchair cases are shown in Figure 3. One can see that in the zigzag loading case, the main bond elongation is experienced by bond B. In the armchair loading case, the main bond elongation is experienced by bond A. When the strain is smaller, the elongation ratio of amchair A is larger than that of zigzag B (see Figure 3(a)). However, the elongation ratio of amchair A become smaller and is lower than that of zigzag B when the strain is larger than 0.1. Moreover, the magnitude of the bond angle variation in the amchair direction tension test is larger
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