13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- first nucleate from the two middle GBs, and their existence are found around all four GBs with further deformation, i.e., the plastic deformation is almost evenly distributed along the four GBs (see Fig. 3d2). Similar as the NW with one GB, a local HCP structure (see Fig. 3d3) is produced during the torsional angle between 2.702 and 2.959 rad, which also causes apparent strain energy resumption as highlighted Fig. 2. This structure is dissolved gradually afterwards. The critical angle is estimated around 0.880 rad for the NW with nine GBs, after which, intrinsic SFs nucleate from the location of GBs (see Fig. 3e1). According to Fig. 3e2, the presence of SFs is found between all GBs, implying the evenly distributed plastic deformation along the NW axis. It is supposed that owing to the small GBS, further propagation of SFs is stopped by GBs, which induces a gradual increasing trend of the strain energy (refer to Fig. 2). To mention that, a local HCP structure is also generated around the middle area of the NW as illustrated in Fig. 3e3. In short, the introduction of GBs has greatly decreased the critical angle, and led to an extremely early yielding comparing with the perfect NW. Additionally, NWs with GBs are inclined to produce a local HCP structure during loading, whose occurrence is detected for NWs with 1, 4 and 9 GBs. 3.2. Polycrystalline nanowire with TBs We then consider polycrystalline NWs that contain different numbers of TBs. Fig. 4 illustrates the trajectory of ΔE with the increase of φ for these different cases. Different with the NWs with GBs (in Fig. 2), the elastic portion of the ΔE-φ curve for all different NWs almost overlaps with that of the perfect NW. Comparing with the critical angle of 1.703 rad, an earlier yielding is observed with the presence of TBs. Particularly, the ΔE-φ curve shows a regular reduction and resumption processes as partially shown in Fig. 4. To unveil the corresponding underlying mechanism, the atomic configurations are extensively investigated. Due to the similarity of plastic deformation, only the snapshots of the perfect NW and NWs with one, three and six TBs are presented in Fig. 5. Figure 4. Strain energy versus curves for NWs with TBs. Figure 5a1-a3 shows the atomic configurations of the perfect NW at three different torsional angles. As is seen, before yielding, the original crystal structure of the NW appears unchanged (see Fig.
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