Multi-stable mechanical metamaterials by elastic buckling instability

The mechanical responses of two novel kinds of two-dimensional (2D) mechanical metamaterials containing opposite or parallel snapping curved (U-shaped) segments with elastic snap-through instability mechanism are systematically investigated. Under uniaxial loading, the metamaterials undergo a large deformation caused by stiffness mismatch between snapping (buckling instabilities) and supporting (relative stiffer/thicker) components, exhibiting very small transverse deformation after every snapping. Based on the multi-stable mechanism, phase transformation/shape-reconfiguration and zero Poisson's ratio are achieved up to large morphological change. Nonlinear mechanical responses including self-recovering snapping and multi-stability enabling snapping behaviors can be generated by tuning the geometric parameters (the relative thickness of the snapping and supporting segments as well as the amplitude of the snapping curved segments). Then topology analysis is carried out to develop the 2D structures to a series of 3D hierarchical configurations from which can be chosen for various engineering conditions with enhanced snapping mechanism. Specifically, multi-stable/shape-reconfigurable tubes and cylinders are designed using the 3D configurations. Besides, one of the 3D metamaterials is developed for functional applications as shock absorber and damper, i.e., the process from fully stretched state to fully compacted state is used to absorb energy and reduce incoming pressure with small stiffness and strength; then the fully compacted metamaterials are used to carry load and attenuate vibration with relative bigger stiffness and strength. This work gives advance to the design, analysis and manufacture of functionally reconfigurable mechanical metamaterials.