# Assessment of Coating Properties in Car Body by Ultrasonic Method
## 4 Discussion
Furthermore, these types of models are easy to implement, and, considering the obtained fitting quality factors, it is possible to confirm the effectiveness of correct evaluation of the proposed models. However, these models do not take into account the effect of the model on the quality factors. Figure 8: Assessment of features importance using \(F\)-test method. Figure 7: Relationship between the reflection coefficient \(|\)r\(|\) of the wave for a different steel surface roughness \(R_{\text{a}}\) and \(R_{\text{z}}\) in reference to putty drying temperature (different markers shape) and generalized stress level (different color); the obtained stresses were aggregated by fixing to levels expressed by closed integer; (**a**) 3D view, (**b–d**) projections on component planes. account unusual situations, as can be seen, for example, in the case of the results of a single-parameter model. In several cases, similar reflection coefficient \(|r|\) values were obtained for clearly different stress values. To improve this situation, it is necessary to use procedures operating based on probability methods or artificial intelligence, and the construction of these types of models require a significant increase in the representation of samples in the studied population. To this end, the authors have already started a broader study, and their results will be presented in the future. Figure 10: Putty coating quality evaluation model based on purity drying temperature \(T\) and reflection coefficient \(|r|\) of wave. Figure 9: Putty coating quality evaluation model based on reflection coefficient \(|r|\). The use of the Rayleigh wave in assessing the width of the putty coating applied to the body sheet has a key advantage, namely access to the component under examination only from the side of the applied putty. Many times, there is no access to the elements of the car body sheet from the inside without first disassembling them or dismantling the interior equipment. Disregarding the measurement in the absence of applied putty, the height of the ultrasonic pulse (amplitude) decreases linearly with an increase in the width of the coating. In view of the above, it can be concluded that the pulse height of the ultrasonic Rayleigh wave is a useful diagnostic parameter when determining the width of a putty coating on a body steel substrate. The conducted research and its results can be a basis for developing a nondestructive method for determining the width of the applied putty coating. Analyzing all the results of the realized correlation studies, one can observe a trend in which, as the curing temperature of the coating increases, its adhesion to the steel substrate also increases, and the value of the reflection coefficient \(\mid\!\!r\!\mid\) of the ultrasonic longitudinal wave decreases. It can also be concluded that both the nondestructive measure of adhesion, which is the reflection coefficient, and the destructive measure of adhesion (the strength of the bond) mainly depend on the coating curing temperature. Studies of the surface roughness profile, as well as the regime during the conduct of the experiment, allow for the exclusion of other factors that could affect the above-described measures of adhesion of the coating to the substrate. The theoretical value of the reflection coefficient \(\mid\!\!r\!\mid\) is in the range from 0 to 1. The values of this coefficient obtained during experimental testing did not reach the limits. The coefficient was in the range of 0.30-0.86. This may be due to both the complex nature of the adhesive bonding and the specifics of the ultrasonic method. The results of ultrasonic measurements depend primarily on the acoustic properties of the material of the substrate and the coating, as well as the quality of the bonding performed.