Early onset of snapping of slender beams under transverse forcing

The hysteretic snapping under transverse forcing of a compressed, buckled beam is fundamental for many devices and mechanical metamaterials. For a single-tip transverse pusher, an important limitation is that snapping requires the pusher to cross the longitudinal axis of the beam. Here, we show that dual-tip pushers allow early-onset snapping, where the beam snaps before the pusher reaches the longitudinal axis. As a consequence, we show that when a buckled beam under increased compression comes in contact with a dual-tip pusher, it can snap to the opposite direction — this is impossible with a single-tip pusher. Additionally, we reveal a novel two-step snapping regime, in which the beam sequentially loses contact with the two tips of the dual-tip pusher. To characterize this class of snapping instabilities, we employ a systematic modal expansion of the beam shape. This expansion allows us to capture and analyze the transition from one-step to two-step snapping geometrically. Finally we demonstrate how to maximize the distance between the pusher and the beam’s longitudinal axis at the moment of snapping. Together, our work opens up a new avenue for quantitatively and qualitatively controlling and modifying the snapping of buckled beams, with potential applications in mechanical sensors, actuators, and metamaterials.

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