## 5 Results and Discussion
### Effect of the Interfacial Strength on the Stress-Strain Law of the Composites  
In order to obtain the influence of the reinforcement-matrix interface properties on the mechanical properties of the SiCp/6061 Al composites, the real particle geometry model with a volume fraction of 10% was used, as shown in Figure 5a. The uniaxial tensile nominal stress-strain curves of the SiCp and 6061 Al composites are shown in Figure 5b. It can be seen that the mechanical properties of the strong interface model were better than the test results. Increasing the interface strength helped to improve the mechanical properties of the SiCp/6061 Al composites. \begin{table}
\begin{tabular}{c c c c} \hline
**Interface** & **Normal Strength (MPa)** & **Tangential Strength (MPa)** & **Critical Fracture Energy (J/m\({}^{2}\))** \\ \hline Weak & 300 & 300 & 60 \\ Medium & 400 & 400 & 80 \\ Strong & 500 & 500 & 100 \\ \hline \end{tabular}
\end{table} 
Table 3: Parameter settings of the different SiCp-6061 Al interfaces. Figure 6a shows the Mises stress (S, Mises) and plastic strain (PE, Max) cloud map with the medium interface strength under the tensile load at each stage. The black part in the cloud map is the cavity left after the element failure was deleted. For the SiCp-reinforced metal matrix composites, the elastic modulus of the hard particles in the matrix and the reinforcement was different, which led to the strain of the hard particles being much smaller than that of the matrix [4]. Therefore, in the plastic strain cloud map, the particles showed a white state without plastic strain. The deformation of the model was divided into three stages: a uniform deformation stage, an interface failure stage, and a matrix damage stage [35]. The nominal stress-strain curves of each stage are shown in Figure 6c. Figure 6b is the crack formation process around the failure particles of the medium strength interface model at moments 1, 2, and 3. In the first stage, the model deformed uniformly during the stretching process. At this stage, the stress-strain curve was relatively smooth, and the Mises stress and plastic strain distribution of the matrix part in the model were more uniform. In the second stage, the interface between the SiCp reinforcement and the 6061 Al matrix began to be damaged. The interface failure led to a decrease in the bearing capacity of the SiCp particles. The 6061 Al matrix near the failure interface also bore most of the load, resulting in a significant increase in the plastic strain. The stress-strain curve began to show obvious jitter. When the uncoordinated deformation of some of the matrix exceeded the deformation ability of the matrix material, the matrix began to be damaged. At this time, in the third stage, the 6061 Al matrix was first damaged near the failure interface, and the damage increased and further developed into a crack. This process continued until the model failed completely, as shown in Figure 6a. During the whole deformation process of the model, the 6061 Al matrix near the SiCp particles experienced three stages: elastic deformation, plastic deformation, and failure fracture, as shown in moments 1, 2, and 3 of Figure 6b, and this was also verified by the fracture morphology shown in Figure 4d. As the interface strength increased, the occurrence of the interface failure was delayed during the tensile deformation process, and the corresponding fracture strain also increased. The strain values at the beginning of the three stages under different interface strengths are shown in Table 4. In the strong interface strength RVE model, the interface fracture phenomenon appeared less than the other two boundary condition models, as shown in Figure 7. The fracture strain (14%) of the strong interface strength RVE model was much larger than the test result (7.2%). The fracture strain (5.8%) of the weak interface strength RVE model was 1.4% lower than that of the test result (7.2%).