## 3 Calculation Results and Discussion
### Influence Mechanism Analysis
#### 3.4.2 Graphene Content Effect  
According to the analysis and research above, the content of graphene had a significant effect on the normal strength but had little effect on the tangential strength and cohesion strength. This phenomenon can be analyzed from the two aspects of the graphene sheet's strengthening on the copper matrix and its force in the copper matrix. Figure 21 shows the distribution of dislocation and dislocation lines inside the copper matrix at the lifting displacement of 0.7 nm for 6.71 at% and the intact monolayer graphene lamellar. In Figure 21a,c, green is a single-crystal copper atom with FCC structure, the red atom is the copper atom on the defect atomic plane, and the red line is the dislocation line, as shown in Figure 21b,d. As can be seen from Figure 21a,b, when the graphene content is 6.71 at%, there are more dislocation lines inside the composite in the process of pulling up, and they are distributed in the upper and lower copper matrix and the copper atoms in the middle part  
Figure 21: Dislocations and dislocation lines under different contents: (**a**) 6.71 at% internal dislocation; (**b**) 6.71 at% dislocation line; (**c**) complete monolayer internal dislocation; (**d**) complete monolayer dislocation line. Figure 20: Pull-up and cohesion simulation system energy. (**a**) Pull-up model; (**b**) cohesion simulation. without graphene. However, when the middle interlayer is complete monocular graphene (Figure 21c,d), the dislocation lines in the composite are few and mainly distributed in the copper matrix above the graphene. This is because, for metal crystals, the dislocation will reduce their mechanical strength. However, with the addition of graphene, dislocation motion in the copper matrix will be hindered and restricted, which is equivalent to metal grain refinement [36]. When dislocation is limited, the perfect interface is easier to form in the composite, and the binding between copper atoms and graphene matrix is stronger, thus improving its normal strength. In addition, with the increase in graphene content, a larger interface will be formed in the matrix, and the obstruction and restriction of dislocation movement in the matrix will be enhanced, resulting in higher interface strength. For pull-out, Figure 22 shows the stress distribution in the unpull-out stage and the partial pull-out stage (pull-out displacement 0.625 nm), Figure 22a,c show the overall stress distribution, and Figure 22b,d show the corresponding stress distribution on the graphene sheet. As can be seen from the figure, for the graphene lamellar, the stress on the right side near the pull-out end is greater, while the stress on the left side away from the pull-out end is smaller. Figure 23 is a schematic diagram of load transfer at the interface during the pulling-out process. It can be seen from the diagram that during the pulling-out process, the unpull part of the graphene sheet will be subjected to the combined attractive and repulsive forces of nearby copper atoms, and the resultant force is almost zero. However, the carbon atoms in the pull-out state or near the pull-out state are only attracted by the copper atoms on both sides of the upper and lower sides, which hinders the pull-out process. Therefore, it can be considered that only carbon atoms in the pull-out critical state contribute to the pull-out force, so the number of carbon atoms in the critical state will determine the pull-out force, which is consistent with the results of [PERSON] et al. [35], who showed that the pull-out force is related to the width of graphene but not to its length. Similar to the rule in this paper that the pull-out force is not affected by the graphene content, the definition of interfacial shear strength shows that when the pull-out force is unchanged, the interfacial shear strength is negatively correlated with the contact area, so increasing the graphene content will lead to a decrease in the interfacial shear strength. Figure 22: Stress distribution at different pull-out displacements.