## 3 Methodology for Measuring Damage in a Metal Matrix Composite and Discussion of Results  
### The Mechanism of Fracture in the Sintered V95\(\backslash\)10% SiC Metal Matrix Composite  
In order to determine the effect of reinforcing particles on the fracture mechanism in the V95\(\backslash\)10% SiC metal matrix composite, cylindrical specimens made from the V95\(\backslash\)0% SiC material and the V95\(\backslash\)10% SiC metal matrix composite were tensile tested at room temperature. The results of the mechanical tests are shown in Figure 4a. The figure shows that the strain to fracture of the composite is higher than that of the sintered material under external tensile stresses at room temperature. The fracture of both materials occurs along the interface boundaries rather than in the material matrix (see Figure 4b,c). A similar fracture of the composite occurs under compressive stresses, this being clearly demonstrated by the composite fracture surface in compression tests of the cylindrical specimens at room temperature (see Figure 5). Figures 4c and 5b show SEM images of the fracture surface with a superimposed maps of the distribution of SiC particles and the composite matrix, which were constructed based on EDS analysis. In these figures, the SiC particles are highlighted in green and the matrix is orange. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Material**} & \multicolumn{2}{c}{**Density, g/cm\({}^{3}\)**} & \multirow{2}{*}{**Porosity, \%**} \\ \cline{2-3} \cline{2-3}  & **Experimental** & & **Calculated** \\ \hline V95\(\backslash\)10\% SiC & 2.85 & 2.86 & 0.30 \\ V95\(\backslash\)0\% SiC & 2.81 & - & 0.12 \\ V95 alloy & 2.82 & - & - \\ \hline \end{tabular}
\end{table} 
Table 1: The density and porosity of the materials. The revealed deformation behavior of the metal matrix composite can be explained by the fact that the interface boundaries between the matrix and a reinforcing particle, as well as the interface boundaries among the matrix particles, were the main centers of fracture. The fracture of the composite did not occur in one stage; it resulted from gradual damage accumulation in the material leading to the appearance of macroracks and subsequent fracture. According to the general ideas of the mechanisms of metallic material fracture [9,33,40], the fracture of the composite under study can be divided into three stages. At the first stage of the fracture of the V95\(\backslash\)10% SiC MMC, submicropores and submicrocracks occur both inside the composite matrix and at the particle interface (see Figure 6, stage I). The composite matrix is plastically deformable and fails by ductile fracture (see Figure 7); therefore, in addition to the formation of new submicropores and submicrocracks in the matrix, the submicropores coalesce and previously formed submicrocracks become blunted, thus turning into submicropores. Then, with a significant deformation of the matrix, the submicropores coalesce, with the subsequent appearance of micropores and ductile microcracks. In parallel with increasing damage in the matrix, the stage of isolated development of microcracks occurs at the interfaces (see Figure 6, stage II). At this stage, sharp wedge-shaped microcracks quickly reach a critical value, above which their development requires no increase in external stresses (self-similarity). The growing microcrack runs into a barrier represented by a reinforcing particle or a matrix particle. A microcrack can overcome this barrier only with an increase in external stresses (see Figure 6, stage III); the microcracks coalesce thereafter to form a crack, and this leads to the final fracture of the composite along the interface boundary. Figure 4: The strain dependence of flow stress under tension at room temperature (**a**); the fracture surface after the tension of the V95\(\backslash\)0% SiC sintered material (**b**) and the V95\(\backslash\)10% SiC metal matrix composite (**c**): orange—the matrix; green—SiC particles.