Curly beam with programmable bistability

Abstract

Bistable beams with prebuckled sinusoidal shape are prominently constructed into mechanical metamaterial unit cells with bi- and multi-stability. While the effects of boundary conditions and thickness on their bistability were more studied, few investigations have been focused on the effect of the beam shape. We systematically created new geometries by adding a second sinusoidal term varying in amplitudes and wavelengths, onto the prebuckled bistable beam shape. Nonlinear large deformation finite element modeling showed effective tuning of the forward and backward forces, snapping energy, and the maximum strain, by the wavelength and amplitude. Decent improvements in the overall stability of their second stable state were observed. The enhancement of the relatively weak snap-through behavior of the single beams was demonstrated by pairing a large variety of curly beams into double-beam configurations. Experimental observations on the 3D printed polylactic acid unit cells strongly supported the simulation results, and demonstrated the possibility of building multistable structures. The design of bistable beams with consistent thickness and comparable overall shapes, yet differing mechanical behavior, has opened up new avenues for the development of bi- and multistable structures in programmable mechanical metamaterials, particularly with materials fabricated at the resolution limit of the respective techniques.