Rate-dependent and delayed snap-through behaviors of viscoelastic metamaterials

Snap-through instability can occur after a significant time delay for some viscoelastic structures under certain loading history; the mechanisms of this phenomenon in viscoelastic metamaterials are still unrevealed. This work uses a combined method of experiments, finite element analysis (FEA), and analytical modeling to investigate the rate-dependent and delayed snap-through behavior of viscoelastic metamaterials. The load-displacement responses under different loading-rates and viscoelastic parameters are illustrated with an emphasis on the programable load capacity and stability via FEA. Experimentally, a viscoelastic metamaterial made of silicone rubber is fabricated through 3D printed molds, and demonstrated for delayed snap-through after creeping under a constant force. The sensitivity of the delayed time to the applied force is presented. A phase diagram with respect to the applied force and material viscoelasticity is constructed to demonstrate different snapping behaviors, including near-instantaneous snapping, delayed snapping at finite time, and no snapping. A discrete model that can capture different snapping modes is developed to provide straightforward understanding of the underlying mechanisms. This work can open up potential novel applications of the tunable delayed snap-through behavior of viscoelastic metamaterials.