# Development of Everting Tubular Net Structures Using Simulation for Growing Structures
## 3 Results
### Dimensional Stability and Net Quality  
The visual characterization of all additively manufactured geometries showed that the printed bar diameter is always smaller than the target diameter, with an average of 12%, a minimum of 10% and a maximum of 16% (exemplary to see in Tables 1 and 2). This deviation has to be considered by defining the construction parameter. The diameter of one single bar exhibits a nearly constant value with a variance of less than 1%. For the simulation, the average value determined was rounded from 1727.58 \(\upmu\)m to 1.70 mm.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Left**} & \multicolumn{4}{c}{**Right**} & \multicolumn{2}{c}{**Average**} & \multicolumn{2}{c}{**Deviation**} \\ \hline Z1\_S3 & 1733 & \(\upmu\)m & 1748 & \(\upmu\)m & 1748 & \(\upmu\)m & 1717 & \(\upmu\)m & **1736.50** & \(\upmu\)m & 12.82 & \(\upmu\)m \\ \hline Z1\_S2 & 1733 & \(\upmu\)m & 1748 & \(\upmu\)m & 1748 & \(\upmu\)m & 1733 & \(\upmu\)m & **1740.50** & \(\upmu\)m & 7.50 & \(\upmu\)m \\ \hline Z1\_S1 & 1717 & \(\upmu\)m & 1702 & \(\upmu\)m & 1702 & \(\upmu\)m & 1702 & \(\upmu\)m & **1705.75** & \(\upmu\)m & 6.50 & \(\upmu\)m \\ \hline \hline \end{tabular}
\end{table}
Table 1: Table of measurement results for diameters of the round tension bars, including average and deviation (target diameter: 2 mm).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{diameter in \(\upmu\)m} \\  & & & & & & radial position & & \\ \hline \multirow{4}{*}{bottom} & & point 1 & point 2 & point 3 & point 4 & point 5 & point 6 \\  & 1 & 1774.99 & 1775.97 & 1733.38 & 1762.5 & 1753.33 & 1725.39 \\  & 2 & 1774.31 & 1765.25 & 1727.85 & 1764.46 & 1750.33 & 1736.64 \\  & 3 & 1772.57 & 1766.62 & 1719.2 & 1769.37 & 1759.4 & 1727.62 \\  & 4 & 1773.49 & 1767.74 & 1725.84 & 1766.04 & 1757.15 & 1730.63 \\  & **average** & **1773.84** & **1768.90** & **1726.57** & **1765.59** & **1755.05** & **1730.07** \\  & deviation & & 226.16 & 231.11 & 273.43 & 234.41 & 244.95 & 269.93 \\ \hline \multirow{4}{*}{middle} & & 1 & 1765.63 & 1765.15 & 1747.41 & 1767.4 & 1761.02 & 1741.52 \\  & & 2 & 1770.81 & 1757.13 & 1754.21 & 1768.66 & 1761.69 & 1734.13 \\  & 3 & 1773.89 & 1764.54 & 1743.29 & 1764.84 & 1760.93 & 1729.44 \\  & 4 & 1776.13 & 17 After performing the functional test on the initial net geometry, fractures appeared on the structure. A detailed visual check identified three failure patterns: most frequently failure was found on geometrical notches at the nodes (Figure 12a) and sporadic failures were found on printing misalignments along printing layers (Figure 12b) and on topological notches (Figure 12c).  
A detailed examination of all nodes using qualitative microscopy and the statistical analysis of the results showed that 80% of the fractures were caused by geometrical notches, as shown in Figure 12a. In Figure 13, the local distribution of the failure patterns is shown. It can be seen that the errors are mainly located in the upper part of the structure. The reason for this is the process of initialization, which requires an enormous expansion of the net. Likewise, the overturning was only done up to half of the total length of the net tube. However, it can be assumed that the geometric notches in particular will lead to damage along the entire structure if the load continues to be applied. Therefore, an improvement of the net geometry using simulation was implemented to increase the repeatability and endurance strength of the net structure.  
Figure 12: Failure pattern on geometrical notches (**a**), on printing misalignments along printing layers (**b**), and on topological notches (**c**).  
Figure 13: Net in unrolled representation: Location of failure pattern on geometrical notches (red), on printing misalignments along printing layers (orange) and on topological notches (blue).