Time-delayed snap-through of hard-magnetic viscoelastic symmetrically pre-curved beams

Snap-through instabilities are widely exploited in nature and engineering to achieve rapid and large deformations. Hard-magnetic soft polymers enable reversible, rapid, and remote triggering of snap-through responses under magnetic stimuli. However, the inherent viscoelasticity of soft polymers introduces pronounced time delays in snap-through dynamics, rendering the response strongly time dependent. The combined effects of viscoelastic dissipation and magnetic actuation on the timing of snap-through remain poorly understood. In this work, we investigate magnetically triggered snap-through behavior in symmetrically pre-curved beams composed of hard-magnetic viscoelastic soft polymers, with particular emphasis on delayed snap-through and delayed snap-back. A magneto-viscoelastic finite element framework, quantitatively validated against experiments, is employed to investigate the magnetically driven, time-dependent snap-through response. Limit point analysis based on a shallow pre-curved Euler–Bernoulli beam model is conducted to interpret the phase diagram of stability. The numerical and experimental results show that beams exhibiting non-latching bistability in the elastic limit can undergo delayed snap-through and delayed snap-back. The delay times are shown to be tunable through the combined effects of viscoelasticity and magnetic loading protocols. These findings establish snap-through timing as a controllable feature and provide guidance for the design of magneto-responsive, temporally programmed snapping structures.