Dynamic buckling of an elastic ring in a soap film

Dynamic buckling may occur when a load is rapidly applied to, or removed from, an elastic object
at rest. In contrast to its static counterpart, dynamic buckling offers a wide range of accessible
patterns depending on the parameters of the system and the dynamics of the load. To study these
effects, we consider experimentally the dynamics of an elastic ring in a soap film when part of the
film is suddenly removed. The resulting change in tension applied to the ring creates a range of
interesting patterns that cannot be easily accessed in static experiments. Depending on the aspect
ratio of the ring’s cross section, high-mode buckling patterns are found in the plane of the remaining
soap film or out of the plane. Paradoxically, while inertia is required to observe these non-trivial
modes, the selected pattern does not depend on inertia itself. The evolution of this pattern beyond
the initial instability is studied experimentally and explained through theoretical arguments linking
dynamics to pattern selection and mode growth. We also explore the influence of dynamic loading
and show numerically that by imposing a rate of loading that competes with the growth rate of
instability, the observed pattern can be selected and controlled.