Non-contact actuated snap-through buckling of a pre-buckled bistable hard-magnetic elastica

Snap-through buckling of bistable structures is a classic topic in mechanics which has been widely studied and applied in various fields such as mechanical meta-materials and soft robotics. Obstacles that hinder broader applications of conventional bistable structures include the requirement of contact actuation to trigger instability and difficulty to control post-buckling configurations. In contrast, hard magnetic elastica (HME), a composite made of hard ferromagnetic particles and soft elastomer that deforms in response to an externally applied magnetic field, exhibits great potential to bring major advances in this field by allowing non-contact actuation and programmable control of snap-through buckling via magnetization distribution (M-distribution). Here, we develop a theoretical framework to trace the instability and post-buckling evolution process of snap-through buckling of a bistable HME. In contrast to the conventional snapping through end-end shortening, the design space for bistable HME includes two key parameters: the remanent magnetization density after premagnetization and the external magnetic field. We focus on two simple yet practical cases: a fixed amplitude of magnetization density along the HME with direction reversed at the magnetization interface (M-interface), and a uniform magnetic field with varied direction. We identify an optimal position for the single M-interface and direction for the uniform actuation field for pre-buckled beams with two-ends fixed, which can reduce the required actuation field for snapping to nearly half in comparison with the symmetric cases. Experiments and finite element analysis are performed to validate the model predictions. Our work may stimulate further studies on utilizing snap-through buckling in applications where fast and large shape transitions from one stable state to another can be actuated in a low-energy, non-contact mode through a remotely applied stimulus field.

Automated summary

Snap-through buckling of bistable structures can be triggered and controlled through deformation caused by an externally applied magnetic field in hard magnetic elastica (HME). The key parameters in the design of HME are the remanent magnetization density after premagnetization and the external magnetic field. Experimental results show that optimal positions of a single magnetization interface and directions of a uniform actuation field can reduce the required actuation field for snapping nearly by half in pre-buckled beams with two-ends fixed.