# Structural and Tribological Analysis of Brake Disc-Pad Pair Material for Cars
## 3 Results and Discussion
The metallographic structure of the brake disc material sample (magnified by 500:1, from the selected area) is presented in Figure 6. According to the chemical composition, it presents a pearlific gray cast iron with 3.34% C, 2.15% Si, 0.64% Mn, 0.03% P, 0.02% S, 0.04% Cr, 0.047%, and Cu, 0.041%, to which other chemical elements are added, such as Ni, Mo, Sn, V, Ti, W, and Sb, in very small amounts that cannot be detected, and the carbon equivalent (EC) \(\approx\) 4.26. The metallographic structure of the brake disc material (Figure 6a) contains pearlite (dark islands), secondary ledeburite (dotted white field), secondary cemite (white areas), fine lamellar graphite (dark lamellar islands), and in the EDS spectrum (Figure 6b), can be seen the chemical elements that make up the chemical composition of the gray pearlific cast iron. Overall, the structure of the pearlific gray cast iron is normal, being free of structural defects. \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Property**} & \multirow{2}{*}{**Metal**} & \multicolumn{3}{c}{**Material**} \\ \cline{3-5}  & & \multicolumn{2}{c}{**Ceramic**} & \\ \cline{3-5}  & & **Volume** & **Fiber** & **Polymer** \\ \hline Tensile strength & G & P & V & G \\ \hline Rigidity & VG & V & VG & P \\ \hline Shock resistance & G & P & V & G \\ \hline Elongation & G & P & VG & V \\ \hline Hardness & G & G & G & P \\ \hline Dimensional stability & G & V & G & P \\ \hline Thermal stability & V & G & VG & P \\ \hline Density & P & G & G & VG \\ \hline Corrosion resistance & P & V & V & G \\ \hline Erosion resistance & G & G & G & P \\ \hline Hygroscopic & V & V & V & G \\ \hline \hline \end{tabular} VG—very good; G—good; P—poor; V—variable.  
\end{table} 
Table 2: Structural performance of composite materials. \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{Flexural strength (MPa)} & \(\bot\) & \(184\pm 25\) \\ \hline \multirow{2}{*}{Compression strength (MPa)} & \(\blacksquare\) & \(144\pm 34\) \\ \cline{2-3}  & \(\bot\) & \(251\pm 48\) \\ \hline \multirow{2}{*}{\(\equiv\) parallelism.} \\ \end{tabular}
\end{table} 
Table 3: Mechanical properties of the composites with metallic constituents for the brake pads. Of great importance is the metallographic and chemical structure of the brake pad material. Thus, the sample from the brake pad, according to the metallographic structure (magnified by 500:1, from the selected area) and the chemical composition is a metal composite with 10% C, 9% O, 1% Na, 5% Mg, 6% Al, 12% Si, 7% S, 2% K, 14% Ca, 6% Ba, 2% V, 5% Cr, 2% Mn, and 19% Fe, as shown in Figure 7.  
Therefore, the metallographic structure of the brake pad material (Figure 7a) contains a lot of metal materials in significant proportions (51% in total), but also carbon in a proportion of 10% (that is, a metallic composite), and in the EDS spectrum, the chemical elements that make up the chemical composition of the metallic composite can be observed (Figure 7b). Overall, the structure of the metal composite is normal and free of structural defects. Regarding the tribological analysis (the behavior of the analyzed materials during the friction and wear process [30]), the role of the metal in the composite friction materials was studied, without being correlated with a mechanism. The study focused on a non-asbestos formula that was added to steel fibers (SF), brass (BF), and copper powder (CP). The total content was balanced with barite to keep the remaining components of the formula constant. The main effect of these metals (demonstrated by the tribological results) is to  
Figure 6: Metallographic structure of the brake disc material (**a**); EDS spectrum of the delimited area (**b**). Figure 7: Brake pad material metallographic structure (**a**); EDS spectrum of the delimited area (**b**). decrease the COF, due to increased speed or load, and Figure 8 shows the effect of speed on the COF.