## 3 Results and Discussion
### Correlations Between Damage Index and Impact Parameters
Taking into account the differences in the peak acceleration values of the impact for the tested surfaces, separate regression models were developed depending on the change in velocity during the impact of the IRD 400 device (Table 3). These were characterized by a high degree of fit, as is demonstrated by the high values of the determination coefficients, which explain 81% to 96.3% of the variability between the peak acceleration \(a\) and the change in velocity _av_. [PERSON] et al. [34] and [PERSON] and [PERSON] [7] considered the mass of the tubers, the height of the fall, and the type of impact surface as the main factors influencing the \begin{table}
\begin{tabular}{c c c} \hline
**Surface** & **Model** & **R-Squared, (R2)** \\ \hline Steel & \(a=-21.10v^{2}+237.78v-195.15\) & 0.662 \\ Concrete & \(a=-71.22v^{2}+575.43v-723.75\) & 0.750 \\ Rod & \(a=-16.38v^{2}+201.63v-282.31\) & 0.755 \\ Bulk potatoes & \(a=-2.3626v^{2}+42.965v-44.56\) & 0.444 \\ \hline \end{tabular}
\end{table} 
Table 4: Dependence of the peak acceleration of the IRD 400 device (_a_) on the initial impact velocity (_v_) for different surfaces together with its statistical evaluation using the coefficient of determination R2. peak accelerations and velocity changes at the moment of impact. The increase in peak acceleration with increasing impact velocity or drop height is a well-known phenomenon observed in many other impact tests [26]. Results from a study on the impact of potato tubers with rods [12] indicated that a higher peak acceleration induced more extensive tuber damage. Studies by [PERSON] et al. [8] showed that 22.7 kg of potatoes placed on the bottom of a cardboard box with a drop height of 15 cm and dropped onto a concrete floor reached a peak acceleration of 200 \(g\). The increase in peak acceleration, including the peak force with increasing impact velocity, supports the hypothesis that peak force and the resulting internal stresses are key elements causing impact damage [38]. The relationship between the IRD 400 peak impact acceleration and the initial impact velocity can be represented by a parabolic formula (Table 4). The evaluation of these regression models is at a lower level because the coefficient of determination values are in the range of 44.4-75.5%. Although a measurement method was developed, there is still a particular risk of random factors reducing the accuracy of the measurement. The change in velocity is an important indicator characterizing the hardness of the contact surface of the impact. It is related to the characteristics of energy absorption by the impact surface. Calculated based on the area under the acceleration curve as a function of time, it characterizes the type of impact surface and the force and acceleration of the impact [3; 24; 35]. It follows that the value of the impact force causing the damage will be influenced by the change in velocity and the peak acceleration. Taking into account the relationships between the peak acceleration a and the change in impact velocity \(\Delta v\) (Table 3), and the peak acceleration \(a\) and the initial impact velocity \(v\) (Table 4), attention was paid to the possibility of a relationship between the initial event velocity \(v\) and the product of the peak acceleration and the change in impact velocity for the surfaces and potato varieties (\(a\times\Delta v\)). For this purpose, a correlation analysis was carried out between these features (Table 5). Based on the analysis, a strong consistency was found between the initial impact velocity \(v\), the peak acceleration \(a\), the change in velocity \(\Delta v\), and the damage index (this effect was explained in the analysis of variance and the detailed analysis using Duncan's test). However, the strongest consistency was observed between the initial impact velocity \(v\) and the product of the peak acceleration and the change in impact velocity (\(a\times\Delta v\)). The correlation coefficient values for these last two factors are in the range of 0.7491-0.8887.