13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 192 87 87 6 6 6 200 100 Fe3C α-Fe y z x 1 2 3 Figure 3. The molecular dynamics models with pre-existing crack along the interface, all dimensions are in Å Due to the complex crystal structure of Fe3C, in this paper, only [110] orientation faces were simulated, as shown in Fig.4. In Fig.4(a), for cementite (Fe3C) with complex trapezius crystal structure, every single cell contains 4 carbon atoms (gray ball) and 12 Fe atoms (blue ball)[14], while Fig.4(b) shows that the interface structure combined with body-centered cubic iron and cementite. X Y Z X Y Z [010] [001] [100] [010] [001] [100] (a) (b) Figure 4. Fe3C unit cell and interface structure schematic drawing 3. Simulation results 3.1. Stress-strain response Fig.5 shows the atomic snapshots of tensile mode failure at temperature of 473K in different strains. The simulation model starts with elastic deformation from its initial state (Fig. 5(a)) to the yield stress at a strain ε= 0.0303. On yielding there is large scale debonding along the Fe3C-Fe interface (Fig. 5(b)). After this the Fe3C-Fe interface progressively degrades (Fig. 5(c)) and carries virtually no load at strain values above 0.1106. (a) Fe3C α-Fe (b) 1 (c) 2 Figure 5. MD snapshots of tensile mode failure of a cracked interface at 473K at strains (ε) of (a) ε= 0.00, (b) ε=0.0397 and (c) ε= 0.0960. Areas of interest are (1) crack initiation and (2) crack progression Selected examples were examined to characterize stress-strain curves dynamics. Average atomic
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