## 3 Calculation Results and Discussion
### Analysis of Interface Cohesion  
According to the cohesion model mentioned above, the cohesive force-displacement relationship curves of the graphene-copper interface at different temperatures can be obtained, as shown in Figure 13.  
As can be seen from the figure, the cohesion-displacement curve at each temperature can be divided into two distinct stages: rising and falling. The co  
Figure 12: Interfacial shear strength–graphene content curve. Figure 13: Cohesion–displacement curves at different temperatures. increases rapidly with the increase in the lifting displacement and reaches the maximum value when the lifting displacement is about 0.04 nm. Subsequently, the curve enters a descending stage, in which the cohesion decreases rapidly at first, then gradually slows down with the increase in pulling displacement, and finally drops to zero when the interface separation displacement reaches about 0.72 nm. In addition, the maximum cohesion decreases with the increase in temperature. When the temperature is 100 K, the maximum cohesion is 49.38 eV/A. When the temperature rises to 1100 K, the maximum cohesion is only 41.56 eV/A. According to Formula (4), the interfacial bonding strength-temperature relationship with intact monolayer graphene can be obtained, as shown in Figure 14.  
As can be seen from the figure, the interface cohesiveness decreases with the increase in temperature, but the rate of decline is different in different temperature ranges. Among them, the interface cohesiveness decreases rapidly below 500 K, and remains basically unchanged between 500 K and 900 K, while the interface strength continues to decline between 900 K and 1100 K, reaching the lowest point at 1100 K.  
In order to study the effect of graphene content on interface cohesion strength, four kinds of composite material models with different graphene content of 62.5%, 75%, 87.5%, and the whole sheet of graphene were established, respectively. The corresponding graphene atomic content fractions were 12.02 at%, 15.02 at%, 18.03 at%, and 21.03 at%, as shown in Figure 15.  
The interface cohesion properties of the above models were simulated respectively at 300 K, and the cohesive force-displacement curves under different graphene contents were obtained, as shown in Figure 16.  
As can be seen from the figure, the curve trend is basically the same under different contents, but the composites with high graphene content have greater interfacial cohesion, including the maximum cohesion of 46.50 eV/A when the whole sheet of graphene (21.03 at%) is included. The maximum cohesion of 18.03 at%, 15.02 at%, and 12.02 at% was 40.14 eV/A, 33.90 eV/A A, and 28.1 eV/A, respectively, which decreased by about 14.7%, 27.1%, and 39.6% compared with the whole graphene. This is because with the decrease in graphene content, the contact area between graphene and copper matrix also decreases, and the number of interacting atoms decreases, resulting in a decrease in maximum cohesion. Figure 14: Cohesive strength–temperature curve. Figure 15: Models of different graphene contents: (**a**) 12.02 at% content; (**b**) 15.02 at% content; (c) 18.03 at% content; (**d**) 21.03 at% content. Figure 17 shows the relationship between maximum cohesion and cohesion strength, and graphene content. It can be seen from the figure that maximum cohesion increases almost linearly with the increase in graphene content. The cohesion strength was almost unaffected by the content. The maximum cohesivity of the model with intact single-layer graphene interlayers increased by 39.6% compared to 12.02 at%, which was consistent with the increase in graphene content, while the change in cohesion strength was only 3.4%, indicating that graphene content had little effect on cohesion strength. According to the analysis, with the increase in the graphene content, the number of carbon atoms interacting with the copper matrix generates more van der Waals forces, thus increasing the maximum cohesion.