This paper develops an origami based mechanical metamaterial with programmable deformationdependent stiffness and shape modulation, leading to the realization of a distant actuation feature.Through computational and experimental analyses, we have uncovered that a waterbomb based tubular metamaterial can undergo mixed mode of deformations involving both rigid origami motion and structural deformation. Besides the capability of achieving a near-zero stiffness, a contact phase is identified that initiates a substantial increase in the stiffness with programmable features during deformation of the metamaterial. Initiation of the contact phase as a function of the applied global load can be designed based on the microstructural geometry of the waterbomb bases and their assembly. The tubular metamaterial can exhibit a unique deformation dependent spatially varying mixed mode Poisson's ratio, which is achievable from a uniform initial configuration of the metamaterial. The spatial profile of the metamaterial can be modulated as a function of the applied far-field global force, and the configuration and assembly of the waterbomb bases. This creates a new possibility of developing a distant actuation feature in the metamaterial enabling us to achieve controlled local actuation through the application of a single far-field force. The distant actuation feature eliminates the need of installing embedded complex network of sensors, actuators and controllers in the material. The fundamental programmable features of the origami metamaterial unravelled in this paper can find wide range of applications in soft robotics, aerospace, biomedical devices and various other advanced physical systems.
In this paper, cross folding of an elastic sheet, a common folding method in packaging a deployable antenna reflective membrane, was studied numerically with the aim of eliminating material failure in the sheet. The deformation, stress distribution, and peak stress of the sheet, as well as the effects of geometrical parameters on those properties were systematically investigated. Then two methods, i.e., central hole method and central slit method, were explored to reduce the peak stress caused by cross folding. A central slit parallel to the first folding crease was found to be most effective in reducing the peak stress.
Large antenna reflectors used in space have to be folded before launching. Silicone rubber is commonly used as antenna material due to its ability to maintain a shape without external supports upon deployment. However, localized vertices could appear during the folding process, which might lead to material yielding and unrecoverable deformation after deployment. In this paper, the cross folding process of a thin elastic sheet, a common folding method in packaging a reflective membrane, was studied numerically with the aim of eliminating material failure in the sheet. The deformation, stress distribution, and peak stress of the sheet and the dependency of those properties on geometrical parameters were systematically investigated. Based on these studies, two methods, i.e., central hole method and central slit method, were explored to reduce the peak stress caused by cross folding. The results showed that a central slit parallel to the first folding crease was the most effective in reducing the peak stress without causing significant damage to the antenna.
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