Contorting a heavy and naturally curved elastic rod

Abstract

We investigate how the configurations obtained from the writhing of a heavy elastic rod are influenced by its intrinsic natural curvature. To this end, we perform a combination of numerics and precision model experiments on the compression or twisting of a thin rod. The ‘softness’ of these single elastic filaments stems from their slenderness (high aspect ratio), which allow for geometrically nonlinear compliant modes that can accommodate large deformations. We uncover the original mechanism that the presence of a body force (gravity in our case) delays the effect of natural curvature, which results from the complex interplay between geometrical constraints, elasticity and weight. We rationalize our experimental results by coupling the predictive power of a numerical method of our own, with classic theory for elastic rods under large deformations. This preponderance of geometry is relevant in systems over a wide range of length scales where curvature and body-forces often co-exist; from engineered rod-like structures such as wires, cables, and pipelines, to natural macromolecules, flagella, fibers and tendrils.