The field of multi-stable structures has been steadily growing due to a wide range of potential applications including energy harvesting, MEMS, and mechanical logic. This work focuses on utilizing elastic energy trapping and snap-through phenomena of bistable unit cells to design a latticed, hierarchical multi-stable cylinder that can articulate up to 30 degrees from its center axis. The employment of bistable elements is hypothesized to reduce the total strain energy required to articulate the cylinder, and yield faster responses with the snap-through. While multi-stable cylinders exist in previous studies, there have been no previous attempts at studying different modes of deformation beyond compressive loading. Thus, the current work presents a new problem regarding the effects of bistable elements in a latticed cylinder that is carrying tensile, compressive, and shear loadings and exhibiting large displacements as the cylinder is articulated. A finite element model is developed to study the influence of a bistable element’s geometric parameters on (i) the force versus displacement curve, and (ii) maximum strain which aid in material selection and  characterization of the unit cell elastic strain energy. Additionally, a latticed cylinder design composed of six rows of unit cells is introduced. In the initial configuration, half of the unit cell rows start in a different position (extended or compacted), enabling axisymmetric bending of the cylinder. As the cylinder bends in any direction, the extended unit cells on the compressive side will snap through to their new compacted configurations while the unit cells in the compacted configuration will be extended on the tensile side. The total strain energy density of the articulating cylinder is investigated as a function of the heights of the unit cells, which aids in determining an ideal height for the design that minimizes the strain energy density. These results will lead to future works on further optimizing the articulating cylinder by varying additional parameters like the individual heights of rows,  the thicknesses of unit cell beams, the strain energy density, and the initial loading threshold for articulation. In addition, the work in this study can yield methodologies for designing arbitrarily morphing skins beyond just cylindrical geometries.


Analysis of Multi-Stable Architectures for Morphing Structures

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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