Equilibrium Shapes with Stress Localisation for Inextensible Elastic Möbius and Other Strips

Abstract

We formulate the problem of finding equilibrium shapes of a thin inextensible elastic strip, developing further our previous work on the Mobius strip. By using the isometric nature of the deformation we reduce the variational problem to a second-order one-dimensional problem posed on the centreline of the strip. We derive Euler–Lagrange equations for this problem in Euler–Poincare form and formulate boundary-value problems for closed symmetric one- and two-sided strips. Numerical solutions for the Mobius strip show a singular point of stress localisation on the edge of the strip, a generic response of inextensible elastic sheets under torsional strain. By cutting and pasting operations on the Mobius strip solution, followed by parameter continuation, we construct equilibrium solutions for strips with different linking numbers and with multiple points of stress localisation. Solutions reveal how strips fold into planar or self-contacting shapes as the length-to-width ratio of the strip is decreased. Our results may be relevant for curvature effects on physical properties of extremely thin two-dimensional structures as for instance produced in nanostructured origami.