# Alternative Solution for Towing Systems Used in the Automotive Industry
## 3 Experimental Results
### Experimental Determinations on Towbar
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **Maximum Force** & \begin{tabular}{c} **Maximum** \\ **Displacement** \\ **[mm]** \\ \end{tabular} & \begin{tabular}{c} **Maximum Stress** \\ **[MPa]** \\ \end{tabular} & \begin{tabular}{c} **Specific Mass** \\ **[Kg/m3]** \\ \end{tabular} & \
\begin{tabular}{c} **Rupture** \\ **YES/NO** \\ \end{tabular} \\ \hline Carbon Fibers & 14,436 & 27.65 & 354.36 & 780 & YES and NO ** \\ \hline Steel S355 & 24,724 & 13.85 & 606.89 & 3.400 & NO \\ \hline Aluminum Al99.7 &
\begin{tabular}{c} 5134 *** \\ 2905 \\ \end{tabular} & 54.60 & 71.31 & 1.050 & NO \\ \hline AlSi10 MnMg & 8504 & 18.80 & 208.74 & 1.050 & YES \\ \hline AlSi12 Cu1 Fe & 7401 & 15.40 & 181.67 & 1.050 & YES \\ \hline \hline \end{tabular}  
In the frame that highlights the specific mass, it should be remembered that both the ball and the bushings near the fixing holes of the carbon fiber towing hook are made of steel, components that considerably increase its mass. ** In the border showing the final state of the towbars (after applying the breaking force), for the towbar made of carbon fiber and epoxy resin, there is the dual information that the product broke and did not break. This paradox arises because the tow hook did not break in the critical area where it was expected to, where the maximum stress resulting from the theoretical calculations occurs, nor in the bonding area between the fibers and the steel ball. It broke in the area of the metal pin located in the part closest to the ball, in the part farthest from the force actuation axis. The mounting holes are tension concentrators (Figure 19). ** In the frame where the maximum force acting on the ball of the towbar made of pure aluminum is highlighted, two forces are noted. The highest force of 5.134 kN appears on the diagram obtained from the test machine, but in the process of testing this hook there was an excessively large deformation, and for this reason the punch of the traction machine moved from the ball to the neck of the hook towing. From this moment, the evolution of the force was accentuated, but without relevance in this study; therefore, the continuation of the characteristic curve specific to this experiment was drawn with a dotted line (Figure 28).  
\end{table} 
Table 5: Experimental measurements of towbars. Figure 28: Superposition of the characteristic curves of the towing hooks. Analyzing the two diagrams in Figures 27 and 28, as well as the values in Table 5, the following can be concluded (through multiple comparisons):  
* The carbon fiber towing hook has up to 60% of the strength of the steel one, and the ball displacement is almost double, making it the strongest hook among the hooks made of alternative materials. * The same carbon fiber hook shows two sudden decreases in strength, which signifies a state of inhomogeneity, either by the detachment of the metal bushings from the carbon fiber structure, or by the local destruction of some groups of carbon fibers; both possibilities are plausible because, according to the experimental determination, detachment of the two bushings from the fiber structure is observed, as well as ruptures of some groups of fibers. * The AlSi10 MnMg towbar has a strength below 35% that of steel, and the displacement is up to 35% higher, this hook having lower performance compared to the one made of carbon fibers, but higher performance compared to AlSi12 Cu1 Fe. * The AlSi12 Cu1 Fe hook shows around 30% of the strength of the steel one, the displacement values of the two products being comparable. * The hook made of Al99.7% is the most deficient in terms of mechanical strength, having a resistance of around 12% of that of the steel hook, but it has an excessively high displacement value, being 3.5 times higher. Since, up to this point in the current chapter, references have been made only to the mechanical strength obtained by each individual towing hook, we believe that the analysis of their specific masses through the same diversity of materials should not be neglected.