The origami waterbomb base is a single-vertex bistable origami mechanism that has unique properties which may prove useful in a variety of applications. It also shows promise as a test bed for smart materials and actuation because of its straightforward geometry and multiple phases of motion, ranging from simple to more complex. This study develops a quantitative understanding of the symmetric waterbomb baseʼs kinetic behavior. This is done by completing kinematic and potential energy analyses to understand and predict bistable behavior. A physical prototype is constructed and tested to validate the results of the analyses. Finite element and virtual work analyses based on the prototype are used to explore the locations of the stable equilibrium positions and the force–deflection response. The model results are verified through comparisons to measurements on a physical prototype. The resulting models describe waterbomb base behavior and provide an engineering tool for application development.
Carbon nanotubes (CNTs) can be grown in dense lithographically patterned forests to form framework structures that can be filled in via chemical vapor deposition to form solid structures. These solid structures can then be used in microelectromechanical systems (MEMS) applications. Initial testing with these structures suggests that when these frameworks are filled with carbon, the resulting material exhibits favorable properties for use in compliant MEMS. To better understand this material's properties, we conducted tests to measure its Young's modulus, failure stress, and stress relaxation in the direction perpendicular to the CNT growth, as well as the modulus and stress in the direction parallel to the CNTs. To determine the properties in the transverse direction, we applied vertical loads to the tips of simple cantilever beam samples, and recorded the force and deflection until failure. The results showed failure strain up to 2.48%. Cantilever samples prepared from the same pattern were also used to measure the stress relaxation of the material. The first test for each sample showed an average force relaxation of 3.72%, while successive tests only produced 1.23% after 24 h. To determine the properties in the direction parallel to the CNTs, we prepared simple rectangular beams and subjected them to 3-point bending tests. The average strain calculated in the parallel direction was 8.17%.[2013-0121] Index Terms-Micromechanical devices, carbon nanotubes, material properties.
The origami waterbomb base (WB) is a single-vertex bistable mechanism that can be generalized to accommodate various geometric, kinematic, and kinetic needs. The traditional WB consists of a square sheet that has four mountain folds alternating with five valley folds (eight folds total) around the vertex in the center of the sheet. This special case mechanism can be generalized to create two classes of waterbomb-base-type mechanisms that allow greater flexibility for potential application. The generalized WB maintains the pattern of alternating mountain and valley folds around a central vertex but it is not restricted to eight total folds. The split-fold waterbomb base (SFWB) is made by splitting each fold of a general WB into two “half folds” of the same variety as the parent fold. This study develops kinematic, potential energy, and force–deflection models for the rigid-foldable, developable, symmetric cases of the generalized WB and the SFWB, and investigates the relative effects of numbers of folds and split-fold panel size, on device behavior. The effect of selected key parameters is evaluated, and equations are provided to enable the exploration of other important parameters that may be of interest in the design and analysis of specific mechanisms. The similarities and differences between the two general forms are discussed, including tunability of the bistable and force–deflection behavior of each.
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