Double restabilization and design of force-displacement response of the extensible elastica with movable constraints

TL;DR

This paper analyzes the complex stability and force-displacement behavior of an extensible elastica with movable constraints, revealing novel double restabilization phenomena and providing analytical tools for designing specific force responses.

Contribution

It introduces the first observation of double restabilization in an extensible elastica and develops an analytical solution for large rotations and strains to aid in shape optimization.

Findings

Identification of single and double restabilization phenomena.

Analytical solution for large deformation behavior.

Design methodology for customized force-displacement responses.

Abstract

A highly deformable rod, modelled as the extensible elastica, is connected to a movable clamp at one end and to a pin sliding along a frictionless curved profile at the other. Bifurcation analysis shows that axial compliance provides a stabilizing effect in compression, but unstabilizing in tension. Moreover, with varying the constraint's curvature at the origin and the axial vs bending rod's stiffness, in addition to possible buckling in tension, the structure displays none, two, or even four bifurcation loads, the last two associated only to the first buckling mode in compression. Therefore, the straight configuration may lose and recover stability one or two times, thus evidencing single and double restabilization, a feature never observed before. By means of the closed-form solution for the extensible elastica, the quasi-static behaviour of the structure is analytically described under large rotations and axial strain. The presented solution is exploited, together with an {\it ad hoc} developed optimization algorithm, to design the shape of the constraint's profile necessary to obtain a desired force-displacement curve, so to realize a force-limiter or a mechanical device capable of delivering a complex force response upon application of a continuous displacement in both positive and negative direction.