Figure A2.
Schematic 2D representation of an elastic element with different stiffness values of εx and εz along the x and z directions, respectively. The blue line at angle α with the z axis represents the structural constraint of the movement of the tip of the element (orange circle) when a force F (blue arrow) is applied. Red arrows: component of the force F along the constraint; green arrow: restoring forces along the constraint, at equilibrium; yellow arrows: restoring forces along the x and z axis; white arrow: projection of F along the z direction. (A) Force F parallel to the z axis. (B) Force F at a generic angle β with the z axis.