Design And Analysis Of Compliant Bistable Mechanism For Multistable Mechanical Metamaterials

Mechanical metamaterial is a kind of man-made structural material,which can exhibit special mechanical properties which are not found in natural materials after reasonable structural design.The source of these properties is usually not caused by the molecular structure of the material itself,but by the mutual formation of micro-structural units with special configurations,which is essentially different from the traditional engineering materials that rely on molecular properties.Multistable mechanical metamaterials have been widely used in the field of mechanical metamaterials because of their multiple stability,adjustable stiffness and negative Poisson’s ratio.Currently,multistable mechanical metamaterials with multi-stable mechanisms as basic cell units have been proved to have special mechanical properties such as large deformation recovery,high specific stiffness and variable Poisson’s ratio,and can capture elastic energy through stable structural deformation,so as to achieve significant vibration isolation,energy dissipation and programmable functions.These unique properties have stimulated the research interest in multistable mechanical metamaterials.The basic unit to construct the multistable mechanism is usually bistable mechanism.Each basic unit of the bistable mechanism has two stable configurations.Once the applied load reaches the threshold value,its configuration will suddenly jump from one stable position to another stable position.In some existing bistable/multistable mechanisms,the steady-state jump between steady-state positions generally occurs in the plane,and the influence of out-of-plane deformation is rarely taken into account,which will limit the application of multistable mechanical metamaterials under complex loads.The unnecessary deformation caused by out-of-plane loads will lead to different kinematic behaviors of compliant bistable/multistable mechanisms,which will affect the mechanical properties of multistable mechanical metamaterials.In order to overcome these shortcomings,this thesis presents the design of bistable mechanism with circular beam instead of traditional straight beam to improve the torsional rigidity of flexible bistable mechanism,and the circular beam bistable mechanism is used as the basic unit to construct the spatial multi-stable flexible mechanism,which enhances the motion consistency of the mechanism.The main work of this thesis is described as follows:(1)To meet the need of anti-out-of-plane deformation of bistable mechanism,a new flexible bistable mechanism of three-stage circular beam based on the circular arc length is proposed in this thesis.By changing the shape of the flexible beam,the torsional stiffness of the flexible bistable mechanism is changed.Finite element model is used to study the jumping behavior of flexible circular beam bistable mechanism under different dimension parameters,and the force-displacement curves of circular beam bistable mechanism and straight beam bistable mechanism are analyzed,and the stability of circular beam bistable mechanism is verified.(2)In order to better reflect the relationship between the structural parameters of the circular beam bistable mechanism and the bistable characteristics(second steady-state position,jump displacement,critical force),a kinematic statical model of the circular beam bistable mechanism was established based on the chain beam constraint model,and the effectiveness of the model was verified by simulation and experiment.Through the simulation and experimental results,the circular beam bistable mechanism is verified to have stronger out-of-plane deformation resistance and better motion consistency under off-axis load.(3)By connecting the circular beam bistable mechanism with the flexible actuator,a flexible multistable mechanism is designed,which can have five stable equilibrium states in space without external load.The statics model of the flexible actuator is established and the stable equilibrium state of the actuator is proved.Subsequently,finite element model and experimental model were used to verify the multi-steady state and non-relay steady-state switching behavior of the mechanism,and different configurations of flexible multi-steady state mechanisms were applied to mechanical logic gates,and the role of the designed multi-stable mechanical metamaterial in data storage and computation was proved.