This paper presents an experimental investigation on the origami patterned cylinder made of Tachi-Miura Polyhedron (TMP) unit cell. The unit cell shows strain-softening behavior under compression load. To analyze the effect of nonlinear behavior on the elastic wave propagation in TMP cylinder, fabrication of metallic origami cylinder and impact test were conducted. The thin metallic structure was fabricated using the vacuum bag method. The pressure was applied evenly to the aluminum facets, which have compliant hinges that behave like torsional springs. The first unit cell of the cylinder structure was connected to the dynamic shaker and the pulse load was applied. To measure the dynamic behavior of unit cells during elastic wave propagation, the stereo pattern recognition (SPR) camera system was employed. The experimental result shows that the compressive wave, induced by impact load, was attenuated due to the nonlinear characteristics of the TMP unit cell. Furthermore, the tensile wave, which emerged later, arrived first on the last unit cell. It means that the tensile wave overtook the compressive wave. The speed of the elastic wave is affected by the stiffness of the structure. Based on the strain-softening behavior of the TMP unit cell, the compressive wave is slower than the tensile wave. It induced the attenuation of compressive impact and overtaking of tensile elastic wave. We can expect that this nonlinear characteristic of the origami-based structure can be applied to the shock mitigation structure.
We investigate a design method on tessellations of Tachi-Miura Polyhedron (TMP), origami-based auxetic mechanical metamaterials composed of bellows-like structures. In recent years, mechanical metamaterials have shown a significant amount of intriguing properties both statically and dynamically. In order to provide design tools for this class of metamaterials in a comparable way to the conventional materials, we utilize three-dimensional Ashby charts with Poisson’s ratio to visualize the mechanical properties. This three-dimensional Ashby chart emphasizes the advantage of origami metamaterials compared to conventional materials while maintaining the comparability of general mechanical properties. We analyze mechanical properties both analytically and experimentally. These methods can pave the way for the further utilization of advanced mechanical metamaterials.
We investigate the extreme wave event in mechanical metamaterials composed of Triangulated Cylindrical Origami (TCO). Specifically, we focused on realizing rogue waves by employing a homogeneous one-dimensional chain constructed from the TCO unit cells. In association with data-driven methods, our numerical simulation suggests the wave focusing on a very limited number of unit cells, which can be potentially realized in the experimental setup. The mechanism of the wave localization using the TCO can be leveraged for efficient energy harvesting purposes in engineering applications.
We demonstrate the vibrational edge mode transfer on the dimer mechanical lattice consists of the Triangulated Cylindrical Origami. The configuration of our dimer lattice can be altered only by twisting the chain, and therefore it does not require any replacement of constituent unit cells. Such in-situ tunable lattice opens the bandgap in the wave dispersion relationships with emerging boundary mode. By twisting the chain excited at boundary mode frequency, our numerical simulation shows high transfer fidelity of the edge state through the lattice. The simple and efficient state transfer can be leveraged for energy manipulation in engineering applications.
This paper proposes a concept of a deployable tubular structure with the Yoshimura pattern based upon a novel folding approach. The developed folding approach is based on the reconfiguration of the Yoshimura tubular structure into the intermediate configurations. All the possible candidates of the intermediate configurations are derived with respect to the design parameters. The structural behavior during the reconfiguration process is analyzed to figure out the driving force for the deployment and the stability of the structure. The deployment of the Yoshimura tubular structure is demonstrated through the prototype with active hinges made with shape memory plastic.
A study has been conducted to evaluate the mechanical performance of various continuous fibers based on 3D printer technology. However, not only mechanical performance but also electromagnetic performance must be considered in aerospace industry. In this study, electromagnetic performance evaluation using a scanning free-space measurement (SFM) system was performed on 3D printed carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) specimens in X-band (8.2 ~ 12.4 GHz). It was possible to measure and analyze the electromagnetic performance of composite specimens made by a 3D printer.
We investigate the impact behavior of the Triangulated Cylindrical Origami (TCO) architecture to determine if it can effectively protect a payload dropped from a height. The TCO architecture inherently exhibits coupled longitudinal and rotational motions. TCO is highly tunable and can offer monostable or bistable characteristics based on its initial geometric configurations such as the height and rotational angle. When monostable TCO unit cells are combined in a chain, they can exhibit interesting rarefaction behavior under impact. Specifically, if one end of the chain is impacted, the initial compressive wave can be overtaken by a tensile wave, such that the other end of the chain can feel tension instead of compression in a counter-intuitive manner. In this study, we begin by designing monostable TCO unit cells that are numerically shown to exhibit rarefaction behavior when constructed in chains. Then, we fabricate plastic TCO unit cell prototypes and apply static compression to these prototypes to verify their monostability and to determine their mechanical properties. These unit cells are then organized in a chain of multiple unit cells that are connected mechanically. The chain is then tested dynamically by dropping it using a custom-made drop tower apparatus. We measure the impact felt by the TCO system by using accelerometers and digital image correlation systems. We find that this origami-based system offers a tunable way to mitigate impact applied to the proof mass, showing great potential as a novel payload impact mitigation system for space applications.
We investigate the extreme wave event in mechanical metamaterials composed of Triangulated Cylindrical Origami (TCO). Specifically, we focus on the realization of so-called rogue waves by employing a homogeneous one-dimensional chain constructed from the TCO unit cells. Our numerical simulation shows the significant energy focusing in the very limited number of unit cells. The wave localization behavior varies as a function of the geometrical parameters of the TCO, which enables us to manipulate the wave localization. The configurability of the wave localization using the TCO can be leveraged for energy harvesting purposes in engineering applications.
We investigate combinatorial search and optimizations on tessellations of Tachi-Miura Polyhedron (TMP), origami-based auxetic mechanical metamaterials composed of bellows-like structures. One of the unique features of TMP is that TMP tessellations can achieve various rigid foldable configurations out of one same design of a TMP cell. In this study, we search for the possible combinations of TMP cells by implementing an efficient search algorithm based on graph theory. This combinatorial search method can be exploited to design programmable structures that are adaptive to varying situations of the outer environment.
The overall mechanical properties of an origami can be programed by its pattern of crease, which introduces various interesting mechanical properties, such as tunable stiffness, multistability and coupled deformations. Once obtaining the knowledge about the properties of the side plates, the creases and the folding procedure, the mechanical response of origami can be completely determined. Therefore, origami with highly designable and tunable abilities offers new possibilities for the metamaterial design. In this research, we aim to combine origami with elastic metamaterials. By introducing the tunable twisting origami structure into the subwavelength-scale resonator design, a three-dimensional elastic metamaterial with low-frequency dynamic performance has been proposed, which, at the same time, has the advantages of lightweight and controllablility. The geometrical nonlinearity of the origami building block is first studied, which indicates that the large structural deformation can be harnessed to tune the effective stiffness of the origami. Further research discovers the quantitative relationship between the overall stiffness and each geometric parameter through the potential energy analysis. Then, the designed origami cell is used as an attachable resonator to control the flexural wave propagation in a metamaterial beam. Finally, both static and dynamic experiments are conducted on the origami cell and the metamaterial beam to verify the tunable stiffness and the on-demand bandgaps, respectively.
We investigate nonlinear wave dynamics in origami-based mechanical metamaterials composed of origami-based structures, specifically the Triangulated Cylindrical Origami (TCO). The TCO structure shows coupling behavior between longitudinal and rotational motions. One of the unique features of the TCO is that the unit cell can exhibit mono- or bistable behavior selectively, which is determined by initial configurations such as height and rotational angle. In this study, we first fabricate physical prototypes made of paper sheets, and conduct compression tests on the prototypes to verify this unique tunable mono-/bistable features. By utilizing this tunability, we design a 1D chain of the TCO unit cells in which mono-/bistable behaviors of each unit cell can be altered by geometric parameters. Then, we analyze wave propagation in this origami-based system numerically by applying impact to the end of the chain. When the monostable configuration is selected for all of the unit cells, our numerical analysis shows that the application of compressive impact creates a tensile solitary wave propagating ahead of the initial compressive wave. In addition, the wave speed of this tensile solitary wave can be manipulated by the configurations of the TCO unit cells. These unique tunable static/dynamic behaviors can be exploited to design engineering devices which can mitigate impact in an efficient manner.
The discovery of topological insulators in materials science revolutionized the concept of wave propagation by giving rise to the existence of edge modes that are immune to backscattering. Similarly, the tunability in waveguiding – including in-situ frequency modifications and path designation – can be highly useful in manipulating energy flow, which still remains an open challenge. Here we investigate topologically tunable mechanical metamaterials based on the quantum valley hall effect (QVHE) by utilizing the bi-stable Stewart platform (SP). Generally, topologically protected wave propagation can leverage two physical mechanisms: the quantum hall effect (QHE) and the quantum spin hall effect (QSHE). Compared to the QHE and the QSHE, the QVHE exploited in this study maintains the time reversal symmetry and can be achieved by using a relatively simple, passive system with one degree-of-freedom. The tunable system we propose and investigate in this study is made of a two-dimensional hexagon crystal and is composed of SPs at nodes connected by linear springs. Each building block can exhibit one of the two stable states of the SP, so that the C6 inversion symmetry of the lattice is broken while C3 symmetry is reserved. By changing the sequence of the bi-stable state in the SP, we can formulate two kinds of unit cells – marked as A and B – with different topological properties. Berry curvatures as well as corresponding eigenmodes are obtained to demonstrate the topological conversion between the two lattices. Then we conduct super-cell analysis by forming a 1-by-20 array of A and B unit cells. Band structure of the super-cell indicates the existence of edge modes over the while band gap, which appear at the interface of A and B unit cells. Based on this tunable property of bi-stable SP, we can easily form S-type and L-type (60 and 120 degree bents) topological paths in the 40-by-40 lattices without breaking the original geometry parameters. We then conduct the numerical simulations with these topological wave guides to verify the topological protection of the valley hall edge states from backscattering. The tunable system we proposed in this paper may pave a possible way to achieving tunability of topological metamaterials.
KEYWORDS: Metamaterials, Manufacturing, Signal processing, 3D microstructuring, 3D modeling, Wave propagation, Numerical simulations, Super resolution, Wave plates, Structural engineering
In this presentation, we propose a novel design of elastic metamaterial that possesses unique anisotropic mass density and hyperbolic dispersion, which enables subwavelength-scale flexural wave manipulation. The metamaterial unit cell is inspired by kirigami, an ancient art of paper cutting and folding. A three-dimensional kirigami microstructure can be obtained by simply cutting and folding a thin metallic plate. By attaching the resonant kirigami microstructures periodically on the top of a host plate, a hyperbolic metamaterial plate can be manufactured without any perforation that degrades the strength of the pristine plate. A theoretical model based on the classic plate theory and mass-spring model is developed to understand the working mechanism of the elastic metamaterial. Dispersion curves are obtained by using an extended plane wave expansion method. An anisotropic effective mass density tensor is retrieved based on effective medium theory, which explains the different couplings between the local resonance of kirigami microstructure and the global flexural wave propagations in the host plate along two in-plane principal directions. Finally, numerical simulation on an elastic hyperlens is conducted to demonstrate the subwavelength-scale flexural wave control and super-resolution imaging abilities. The advantages of the proposed kirigami-based elastic hyperbolic metamaterial are twofold: (i) simple manufacturing process without perforation in the pristine plate and (ii) subwavelength flexural wave manipulation providing a high signal-to-noise ratio in plate-like engineering structures. Therefore, the proposed elastic hyperbolic metamaterial could be highly promising for high resolution damage imaging in nondestructive evaluation and structural health monitoring.
We investigate wave dynamics in origami-based mechanical metamaterials composed of bellows-like origami structures, specifically the Tachi-Miura Polyhedron (TMP). One of the unique features of the TMP is that its structural deformations take place only along the crease lines, therefore the structure can be made of rigid plates and hinges. By utilizing this feature, we introduce linear torsional springs to model the crease lines and derive the force and displacement relationship of the TMP structure along the longitudinal direction. Our analysis shows strain softening/hardening behaviors in compression/tensile regions respectively, and the force-displacement curve can be manipulated by altering the initial configuration of the TMP (e.g., the initial folding angle). We also fabricate physical prototypes and measure the force-displacement behavior to verify our analytical model. Based on this static analysis on the TMP, we simplify the TMP structure into a linkage model, preserving the tunable strain softening/hardening behaviors. Dynamic analysis is also conducted numerically to analyze the frequency response of the simplified TMP unit cell under harmonic excitations. The simplified TMP exhibits a transition between linear and nonlinear behaviors, which depends on the amplitude of the excitation and the initial configuration. In addition, we design a 1D system composed of simplified TMP unit cells and analyze the relationship between frequency and wave number. If two different configurations of the unit cell (e.g., different initial folding angles) are connected in an alternating arrangement, the system develops frequency bandgaps. These unique static/dynamic behaviors can be exploited to design engineering devices which can handle vibrations and impact in an efficient manner.
The integrity of thermal protection systems (TPS) is crucial to ensure a successful mission of space exploration vehicles. In this paper, an attenuation-based built-in diagnostic technique is demonstrated through a carbon-carbon (C-C) panel for the detection of bolt loosening under extreme environments. The proposed technique is based on the attenuation properties of propagating waves, which depend on the torque level and contact material at the bolted-joint interface. A smart washer was developed with an embedded piezoelectric element used as an actuator to generate the propagating waves as well as a sensor to receive the diagnostic waves. The washers were installed in each bolt on the TPS panel. During the course of the investigation, a complete diagnostic system including smart washers, diagnostic algorithms, and electronic hardware was developed to verify the proposed attenuation technique.
Experiments which simulate the acoustic environments during the re-entry process were conducted using a shaker in the AFRL to verify the technique. The test results revealed that the proposed system successfully identify the bolt loosening and failure. More tests are being considered to include temperature effect.
Space vehicles require high performance thermal protection systems (TPS) that provide high temperature insulation capability with lower weight, high strength, and reliable integration with the existing system. Carbon-carbon panels mounted with bracket joints are potential future thermal protection systems with light weight, low creep, and high stiffness at high temperatures. However, the thermal protection system experiences a very harsh high-temperature and
aerodynamic environment in addition to foreign object impacts. Damage or failure of panels without being detected can lead to catastrophe. Therefore, knowledge of the integrity of the thermal protection system before each launch and reentry is essential to the success of the mission. The objective of the study is to develop a built-in diagnostic system to assess the integrity of TPS panels as well as to lower inspection and maintenance time and costs. An integrated structural health monitoring system is being developed to monitor the TPS panels. The technology includes investigation of the loosening of bolts which connects TPS panels to the supporting structure, and potentially, identifying the location of damage on the panel caused by external impacts from micrometeorites and other objects. The first generation prototype was manufactured and tested in an acoustic chamber which simulated a re-entry environment to investigate the
feasibility of the health monitoring system focusing on its survivability and sensitivity. The preliminary results were very
promising. Based on the test results, the second generation design was proposed to improve the performance of the first generation design. To put a reliable and accurate decision on the diagnostics of the TPS panels, an advanced algorithm was developed with the aid of a wavelet transform technique.
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