# Assessment of Coating Properties in Car Body by Ultrasonic Method
## 3 Results
### Correlational Research  
Based on the results obtained from the roughness profile measurements of all samples used in the correlation study, it can be concluded that values reflect the same surface preparation. In the case of the \(\mathrm{R_{a}}\) parameter, its value in most cases ranges from 0 to about 1 \(\mathrm{\SIUnitSymbolMicro m}\). There are isolated cases where the value of the arithmetic mean deviation of the roughness profile from the average value is higher. This difference did not significantly affect further ultrasonic and strength tests. Also, in the case of the second tested parameter of the roughness profile, increased \(\mathrm{R_{z}}\) values were observed in several samples. For most of the samples, the value of this parameter ranged from 3 to 8 \(\mathrm{\SIUnitSymbolMicro m}\). In conclusion, the roughness profile studies confirmed that the prior preparation of the surface of the samples allow, in most cases, for the obtainment similar surface properties. In the case of coatings cured at 20 \({}^{\circ}\)C, it can be seen that the reflection coefficient \(\left|\right.\left|\right.\left|\right.\) ranges from 0.63 to 0.87. The adhesion determined from strength tests ranges between 1.51 and 3.25 MPa. Among all the samples, one was rejected due to the phenomenon of decohesion during the destructive test, while the results of two others differed significantly from the others, which may suggest the presence of errors during the implementation of measurements. The aggregate results obtained for samples cured at 20 \({}^{\circ}\)C are summarized in Table 2. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline
**Width [mm]** & **No Coating** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** & **12** & **13** \\ \hline Amplitude [\%]—average value & 99 & 48.6 & 41.4 & 37.8 & 36 & 34.2 & 32.2 & 29.6 & 27 & 26.1 & 24.3 & 22.5 & 19.8 & 15.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of ultrasonic test of car putty coating width. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **\(\mathrm{R_{a}}\)** & **\(\mathrm{R_{z}}\)** & **Reflection Coefficient** & **Force [N]** & **Stress [MPa]** \\ \hline
20.1 & 0.659 & 4.220 & 0.729 & 459 & 2.28 \\
20.2 & 0.837 & 5.910 & 0.631 & 653 & 3.25 \\
20.3 & 0.499 & 2.855 & 0.772 & 422 & 2.10 \\
20.4 & 0.429 & 3.315 & 0.866 & 342 & 1.70 \\
20.5 & 0.588 & 4.055 & 0.668 & 283 & 1.41 \\
20.6 & 0.531 & 3.955 & 0.729 & 577 & 2.87 \\
20.7 & 0.369 & 2.860 & 0.516 & 399 & 1.99 \\
20.8 & 0.626 & 4.145 & 0.729 & 539 & 2.68 \\
20.9 & 0.909 & 6.525 & 0.631 & 78 & 0.39 \\
20.10 & 0.419 & 3.600 & 0.818 & 303 & 1.51 \\ Average & 0.586 & 4.144 & 0.709 & 405.5 & 2.018 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of ultrasonic and mechanical test for samples cured at 20 \({}^{\circ}\)C.  
Samples with coatings cured at 40 \({}^{\circ}\)C show better adhesion than those that were cured at 20 \({}^{\circ}\)C. It reaches between 3.48 and 5.38 MPa. These results correspond to the determined value of the reflection coefficient in the range of 0.7-0.8. The results obtained for sample 40.10 were rejected in Section 4, due to the low value of the |r| coefficient (0.266), which differed significantly from others in this measurement series. The aggregate results of the measurements for the coating cured at 40 \({}^{\circ}\)C are summarized in Table 3. Putty coatings cured at 50 \({}^{\circ}\)C are characterized by adhesion in the range of 4.56-7.60 MPa. On the other hand, the results of ultrasonic testing revealed |r| coefficient values ranging from 0.516 to 0.613 (Table 4). The fourth measurement series included samples cured at 60 \({}^{\circ}\)C, in which putty coatings achieved the best adhesion to the steel substrate (7.32-18.97 MPa). These values corresponded to a reflection coefficient |r| in the range of 0.299-0.398 (Table 5). In contrast to the other measurement series, the fourth series contained as many as two samples in which the phenomenon of decohesion occurred.