13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- To investigate the influence of interfacial region’s mechanical properties on the elongation of multilayered composites, we consider three different types of interatomic bonding strengths between the M-D and M-B phases. The interaction between the M-D and M-B phases φBD(r) is calculated by ( φB(r) + φD(r))/A, where A = 1 (strong bonding strength), A = 2 (normal bonding strength), or A = 5 (weak bonding strength). 3.2. Influence of Interfacial Mechanical Properties on Mechanical Properties of Multilayered Composites Figure 3 shows the stress–strain curves for single-phase materials and multilayered composite materials with different interfacial bonding strengths. The multilayered composites demonstrate a better combination of strength and elongation than the single-phase materials. It is also apparent that the stronger the interfacial bonding, the larger the peak stress on the multilayered composite model. However, for the elongation, we can see the opposite tendency. Figure 3. Stress–strain curves of multilayered composites with different interface strengths. Figure 4 shows the plastic deformation phenomena around the interfacial region with different mechanical properties. Atomic color represents the shear stress component. First, dislocations in the ductile phase move toward the interface in cases of both A = 1 and 5 when ε=0.02. In the case of the weak bonding strength of A = 5, the dislocations are impinged into the interface and further plastic deformation does not occur from the interface. Therefore, initiation of plastic deformation in the brittle phase is delayed. These results show that it is difficult for dislocations from the ductile phase to transmit through the interface when the interfacial region has a weak bonding strength. Consequently, the multilayered model with A = 5 shows high peak stress but small elongation owing to the cleavage of the brittle phase under large tensile stress by stress partitioning between the brittle and ductile phases (see Fig. 4(a)). On the other hand, in the case of a strong bonding strength of A = 1, dislocation emissions can easily propagate from the interface, and thus, plastic deformation propagation occurs from the ductile to brittle phases across the interface. The stored
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