Snap-through mechanism of an elastic bimetal ring for rotary actuation

Abstract

Smart materials responsive to stimuli and new rotary mechanisms have drawn much attention in recent years. This paper investigates a novel snap-through rotation mechanism of a thermal responsive bimetal ring confined inside the annular region constraint when subjected to the local curvature induced by thermal loading. The buckled ring has movable boundaries and keeps an invariant shape during the snap-through rotation so that it requires small energy input to drive the bistable transition. To uncover the elusive mechanism behind this intriguing snap-through phenomenon, a theory based on the bifurcation and energy principle is developed to predict the critical loading curvature and the critical loading temperature, which agrees with the experimental results. The effects of loading positions and the constraint width are studied and a map predicting the critical loading curvature with different geometrical parameters is demonstrated. The rotary buckled ring not only enables the bistable actuation, but also triggers various actuation applications such as the motor actuation and the pump actuation. Due to great advantages in terms of energy supply and actuation loading, this study exhibits great potential of the proposed snap-through mechanism in bistable structures and rotary actuation.