The elastica sling

TL;DR

This paper investigates the nonlinear mechanics and stability of a flexible elastic rod constrained by sliding sleeves, revealing conditions for stable configurations and demonstrating potential applications in energy harvesting and soft robotics.

Contribution

It extends stability analysis to variable-length elastica systems and introduces the elastica sling concept with experimental validation.

Findings

Maximum of one stable equilibrium configuration exists.

Critical inclination pairs cause loss of stability.

Experimental results confirm theoretical predictions.

Abstract

The nonlinear mechanics of a flexible elastic rod constrained at its edges by a pair of sliding sleeves is analyzed. The planar equilibrium configurations of this variable-length elastica are found to have shape defined only by the inclination of the two constraints, while their distance is responsible only for scaling the size. By extending the theoretical stability criterion available for systems under isoperimetric constraints to the case of variable domains, the existence of no more than one stable equilibrium solution is revealed. The set of sliding sleeves' inclination pairs for which the stability is lost are identified. Such critical conditions allow the indefinite ejection of the flexible rod from the sliding sleeves, thus realizing an elastica sling. Finally, the theoretical findings are validated by experiments on a physical prototype. The present results lead to a novel actuation principle that may find application as a mechanism in energy harvesting, wave mitigation devices, and soft robotic locomotion.