snapthrough

Snapthrough is an elastic instability in which a structure with two or more stable equilibrium configurations undergoes a rapid transition from one configuration to another as a control parameter is varied. It is commonly observed in bistable elements such as curved beams, shallow arches, and spherical shells, where the load–deflection response becomes nonmonotonic and a critical change in load or displacement causes a sudden jump to a different stable state. The transition may be triggered by quasistatic loading or by dynamic effects when stored elastic energy is released.

Mechanism and energy perspective: In bistable geometries, the system sits at a local minimum of potential energy corresponding to one configuration. As a parameter changes, the energy landscape evolves until the minimum and a neighboring minimum become connected through a rapidly changing path, often via a saddle point. When the barrier separating the equilibria vanishes at the critical value, the structure snaps to the other stable configuration, sometimes with high speed and significant kinetic energy.

Mathematical description: Snapthrough can be analyzed with nonlinear plate or shell theory, energy methods, and bifurcation analysis. The phenomenon is associated with a saddle-node (fold) bifurcation in the equilibrium equation, where two solutions merge and annihilate, leaving the system to transition to a different stable branch.

Applications and examples: Snapthrough is exploited in deployable structures, bistable micromechanical switches, energy harvesting devices, and rapid actuators. It also appears in biological systems and soft robotics, where fast shape change is advantageous.

See also: buckling, bistability, energy barrier, bifurcation.