## 4 Discussion  
In this paper, a pear-shaped fruit FE model was developed and evaluated with the experimental impactor drop test of pear fruits in order to identify bruises. The FE model was validated with the experimental model, resulting in low error values not exceeding 4% and 26% for internal impact energy and bruise susceptibility, respectively. Furthermore, the energy activity summary of explicit dynamics-based simulations can be an indicator for assessing the accuracy of the FE model [7; 12]. Energy activity, including internal, kinetic, hourglass, and contact energy of the pear fruit drop impact, are illustrated in Figure 13. Internal energy is transferred to kinetic energy at the beginning of impact; then, kinetic energy starts to decline and is transferred to internal and contact energy at the highest impact point. Hourglass energy, also called zero-mode energy, is a deformation that does not produce volume or strain change in hex/quad meshes in a finite element model. The literature suggests that hourglass energy should not exceed 5-10% of internal energy [11; 33]. In our simulation scenarios, hourglass energy did not exceed 10% of internal energy values. Therefore, we can say that our FE model is considered accurate. Figure 13: Energy activity summary for pear fruit drop simulation. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Pitch (mm)** & **Number of Revolutions** & **Diameter (mm)** \\ \hline
7 mm & 1 & 57 mm \\ \hline
7 mm & 10 & 57 mm \\ \hline
2 mm & 11 & 49 mm \\ \hline
2 mm & 12 & 30 mm \\ \hline
2 mm & 13 & 20 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Proposed design parameters. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Drop Height**} \\ \hline  & \multicolumn{5}{c}{**0.5 m**} & \multicolumn{5}{c}{**1 m**} \\ \hline  & **Pear Fruit Only** & **Pear Fruit with** & **Percent** & **Pear Fruit Only** & **Pear Fruit with** & **Percent** \\  & **Design** & **Improvement** & **Pear Fruit Only** & **Design** & **Improvement** \\ \hline Bruise Volume (m\({}^{3}\)) & \(1.49\times 10^{-5}\) & \(7.42\times 10^{-6}\) & 50\% & \(5.24\times 10^{-5}\) & 4.14052 \(\times 10^{-5}\) & 21\% \\ \hline Bruise Mass (kg) & \(1.99\times 10^{-2}\) & \(9.93\times 10^{-3}\) & 50\% & \(6.98\times 10^{-2}\) & \(5.52\times 10^{-2}\) & 21\% \\ \hline Bruise Susceptibility (m\({}^{3}\)J\({}^{-1}\)) & \(1.94\times 10^{-5}\) & \(1.10\times 10^{-5}\) & 43\% & \(3.45\times 10^{-5}\) & 3.01743 \(\times 10^{-5}\) & 13\% \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Bruise volume, mass, and susceptibility using the proposed design versus free pear fruit. The FE model can be adopted to develop a packaging structure for pear fruits in order to minimize fruit bruises and protect them from mechanical damage. The proposed design is made of recycled PET plastic, which is spiral-shaped and can absorb the energy of pear fruit at impact drops. Design experiments and response surface methodology were performed to study the influence of spring design parameters on pear fruit bruise susceptibility and behavior. According to RSM results, it was found that spring pitch and thickness have a significant impact on fruit bruises compared with a number of spring revolutions. An optimal design was proposed, proving its ability to reduce bruises of fruit, comparing it to freely dropping a pear fruit on the floor. The proposed packaging design considered the following aspects:  
* Sustainability: The design proposed is made up of 3D printed recycled PET water bottles plastic, which helps achieve a circular economy and reduce greenhouse gas emissions [34]. Furthermore, the design is not disposable, and consumers can reuse the packaging. This would narrow and close loops in the supply chain. * Physical design considerations: The design allows for ventilation thanks to its spring-based design, where air is permitted so that the quality of fruit is assured and shelf-life is extended [35].