# Development of Everting Tubular Net Structures Using Simulation for Growing Structures
## 3 Results
### Preliminary Study of Net Parameters
The explicit solver with single-precision was used in LS-Dyna R11.0.0 winx64 (SMP type) to perform the computations on an eight-core desktop PC. Figure 10 shows the results of the three geometry variation simulations (main variable \(\alpha=[30^{\circ},45^{\circ},60^{\circ}]\)) as a comparison of equivalent von Mises stress distribution of the three models along everting simulation time. Each column (Figure 10a-c) represents a single model with results of four simulation times. The times were recorded at equal simulation points and hence loading stages (rows in Figure 10). The model with the main angle of \(\alpha=30^{\circ}\) (Figure 10a) shows a very unstable evert behavior due to the highest structural stiffness against everting. In the initial everting stage, the structure below the everting zone is equally deformed (angles \(\alpha\) and \(\beta\)) until a critical structural stiffness is reached; the whole tube shows an unstable deformation behavior in simulation after evert-buckling in the initial stage. Furthermore, in the initial everting stage, high equivalent von Mises stresses of about 4 MPa (4 N/mm\({}^{2}\)) occur in the simulation. Figure 10b shows the same everting process with an angle of \(\alpha=45^{\circ}\) between the bar and horizontal axis. The initial stage is characterized by more stable everting behavior. Nevertheless, the deformed bar structure below the evert zone possesses a high stiffness. The elastic energy is mainly stored in the uneverted free zone below. The initial everting takes place after the structural stiffness of the tube below the everting zone is higher than the stiffness in the deformed everting zone. The observed average von Mises equivalent stress amounts to 2.5 MPa (2.5 N/mm\({}^{2}\)). Further continuous everting takes place under stable conditions. Minor buckling on the free tubular surface below the evert-buckling zone was recorded. The third model with an angle of \(\alpha=60^{\circ}\) shows very easy initial evert-buckling due to reduced structural stiffness against the nodal motion. Higher global instabilities can be seen, but in the initial phase, the everting behavior is the best of the three models. In the later continuous everting stage, some buckling in the region of still uneverted structures occurs. However, a stable continuous everting is possible. The average von Mises stress amounts to 0.8 MPa (0.8 N/mm\({}^{2}\)). The strain in the everting zone follows directly from the stresses, due to assumed linear-elastic material behavior. Strain peaks of 0.12 for a net angle of 60\({}^{\circ}\) up to 0.16 for an angle of 30\({}^{\circ}\) arise in the everting zone (Figure 11). The model with a net angle 30\({}^{\circ}\) shows a very unstable everting process (pl. see Figure 11a). Figure 10: Equivalent von Mises beam stress distribution in everting simulation: net angle 30\({}^{\circ}\) (**a**), net angle 45\({}^{\circ}\) (**b**) and net angle 60\({}^{\circ}\) (**c**). Different stages of the everting process are shown from top to bottom for each net angle (columns) at equal times (rows).