## 3 Results
### Uniaxial Tension  
The stress-strain curves for the composites obtained with different potentials are presented in Figure 3. Again, the results observed for the CG-Cu\({}_{BOP}\) composite were different from the other two potentials. Analysis showed that the elastic regime can be defined before \(\varepsilon=0.06\) for all structures (see the insert in Figure 3). After this, the slope of the curve changes, though is still close to a linear regime. The transition to the plastic deformation took place at higher stresses (about 90 GPa) for CG-Cu\({}_{BOP}\) in comparison to CG-Cu\({}_{EM}\) and CG-Cu\({}_{M}\) (which were about 60 GPa). The elastic modulus obtained with the EAM-Morse and Morse potentials were very close \(-267\) and 268 GPa, while, for composite fabricated with the BOP potential, the elastic modulus was almost two times higher \(-487\) GPa.  
The stress-strain curves for CG-Cu\({}_{EM}\) and CG-Cu\({}_{M}\) are coincident up to \(\varepsilon=0.22\). Since the Morse potential is used in these two structures to describe the Cu-C interaction, the only difference is in the description of the Cu nanoparticles. Therefore, these curves are in good agreement. It is also important to note that, for all three structures, the transition from elastic to plastic deformation occurred at \(\varepsilon=0.22\). This is not the maximum value since the composite can be stretched further. However, in the present investigation, the main goal was to understand the effect of the potential function used on the process of composite fabrication.  
It should be noted that all the obtained composites had high strength and ductility. After \(\varepsilon=0.8\), the stress-strain curves for all the composites were very close; no fracture took place before \(\varepsilon=2.5\).  
In Figure 4, the distribution of Cu atoms in the composite before (\(\varepsilon=0.0\)) and after tension (at final state \(\varepsilon=2.5\)), and in the graphene network, are presented separately.  
After compression for CG-Cu\({}_{BOP}\), the Cu nanoparticles remained almost the same as after exposure, occurring as spherical particles of an approximately round shape. In comparison, for CG-Cu\({}_{M}\), already melted nanoparticles and Cu atoms were spread over the structure. Since EAM resulted in higher interaction energy for Cu-Cu, Cu nanoparticles can still be seen in the structure, but already melted, or pre-melted.  
For CG-Cu\({}_{BOP}\) obtained with the BOP potential, the metal nanoparticles remained in a crystalline order and appeared as metal clusters with a size larger than the initial state. Even during tension, the Cu nanoparticles interacted and coagulated to form bigger clusters. Cavities for the Cu nanoparticles can be seen in the snapshots of the graphene network. For CG-Cu\({}_{EM}\) and CG-Cu\({}_{M}\), the Cu atoms were almost uniformly distributed in the graphene network during tension, spreading over the graphene flakes in both cases. This resulted in the formation of a more uniform graphene network.  
It can be concluded that the main difference in the results obtained with the BOP and EAM-Morse/Morse potentials was observed in the elastic regime. The composites obtained from the graphene networks filled with Cu nanoparticles are very promising because they show high strength and ductility. However, different treatment temperatures should be considered for the development of composite fabrication under hydrostatic compression.  
Figure 3: Stress-strain curves for composites under tension. The insertion shows the elastic regime and elastic modulus.