Inflation and instabilities of a spherical magnetoelastic balloon

Abstract

This study explores the instabilities during the axisymmetric inflation of an initially spherical magnetoelastic balloon, modeled as a magnetizable Ogden material, under combined internal pressure and a non-uniform magnetic field generated by current-carrying coils. The nonlinear interplay of geometric and material effects leads to governing equations sensitive to bifurcations and instabilities. A coordinate singularity at the poles of the balloon is identified within the system of governing differential equations, which is resolved through an appropriate choice of field variables and L’Hôpital’s rule. Stability analysis reveals that as inflation progresses, axisymmetry is broken through a supercritical pitchfork bifurcation, resulting in a pear-shaped equilibrium. This symmetry is later restored through a reverse subcritical pitchfork bifurcation, forming an isolated loop of pear-shaped solutions containing stable and unstable branches in the case of a six-parameter Ogden material model (SPOM). The onset of symmetry-breaking bifurcations is influenced by material parameters and magnetic field intensity, with critical values beyond which such bifurcations are suppressed. Both symmetry-preserving and pear-shaped configurations are stable under small asymmetric perturbations in both magnetic and non-magnetic cases. Snap-through transitions between pear-shaped and axisymmetric configurations are also observed.