Fig. 4.

Zipper, aligned, and internally coupled tubes used as cantilevers. (A) Initial (red line) and deformed geometry of the structures at 70% extension when the left end is fixed and a uniform load is applied on the right end. The deformed shapes are scaled so the maximum displacement for each case is equal to the panel height ($a=1$) and do not necessarily represent stiffness. (B–D) The stiffness (force/length) of the cantilevers in the three Cartesian directions. The internally coupled tube cannot extend beyond 80% extension of the external tube. (E–G) The stiffness for loads in the $Y-Z$ plane represented as a radial plot at extensions of 40%, 70%, and 95%, respectively. Stiffness is shown as distance from the origin.