13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- elastic energy in the brittle phases can be released by the plastic deformation. Therefore, it is not easy to reach the critical stress for the cleavage fracture in the brittle phase (see Fig. 4(b)). As a result, the multilayered model with a strong interfacial bonding strength, namely with the interface having the role of the dislocation source, shows much better ductility than the model with a weak interfacial bonding strength. These results imply that it is important to control the interfacial structure to design the multilayered composite metals with coexistence of strength and ductility. Figure 4. Plastic deformation phenomena around the interface with different mechanical properties. 3.3. Discussion Heavily drawn pearlitic steel wires having high tensile strength but small elongation exhibit cementite decomposition at the vicinity of the interfacial region. On the other hand, cold-drawn pearlitic steel aged at 698 K exhibits large uniform elongation [2] and the cementite decomposition recovers. This suggests that the interfacial structures between cementite and ferrite phases change by cementite decomposition due to the equilibrium interfacial structure having the maximum solubility of carbon in both phases. In particular, the role of the interface in plastic phenomena in heavily drawn pearlitic steel wires could change from that in aged pearlitic steel. In our atomic simulations, the multilayered composite model, having a small dislocation source ability of the interface, showed a smaller elongation property than the model having a high dislocation source ability of the interface. This result implies the possibility that the interface structure after cementite decomposition also has a smaller dislocation source ability than that of aged pearlitic steels. 4. Conclusion We investigated the influence of interfacial mechanical properties on the elongation of multilayered composite metals through molecular dynamics simulations. We designed two-dimensional virtual materials having brittle or ductile properties by controlling the parameters of the Morse interatomic potential. We demonstrated that multilayered composite models with ductile and brittle phases have a superior strength–ductility relationship than single-layered models and that this relationship is closely related to interfacial mechanical properties. These results imply that it is important to
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