Modeling and design of a SMA self-actuating bistable beam

Bistable beams with implanted actuators show the self-actuating ability that further improve performance of the system. In this paper, a novel self-actuating bistable mechanism coupled by elastic straight beam and SMA curved beam was designed and tested. Snap-back behavior of the presented system was triggered by SMA curved beam actuator, which generated actuation moment and rotation angle at the end of flexible beam. The bistable mechanism was modeled through nonlinear governing equation of large deflection beam. A solution strategy that considered multiple inflection points was developed to solve the governing equation. Loading path, deflection curves, and energy landscape of bistable beam were illustrated and further analyzed. Moreover, parameters of SMA curved beam actuator were determined by a simplified model. A prototype of the self-actuating bistable beam was fabricated and the snap-back phenomenon was observed on the test bench. Accompanied by the snapback, a 44% decrease of axial load could be reached. It was also found that the bistable beam could be reset by applying vertical concentrated force. Reciprocating snap-back tests were conducted to confirm that point. Possible applications of the presented bistable beam could be variable load mechanisms and novel flexible switches.