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• Proposing an efficient DEM-building method for accurate beam vibration simulation. • DEM is built from continuum beam theory and the dispersion curve of a periodic chain. • The DEM can be expanded to cover a broad frequency range without limitation. • A graded cylinder chain having a broad frequency bandgap is designed. • Superimposing local resonances in beams efficiently forms a wide frequency bandgap. We propose an efficient method to build a simple discrete element model (DEM) that accurately simulates the oscillation of a continuum beam. The DEM is based on the Timoshenko beam theory of slender cylindrical members and their corresponding wave dynamics in assembly. This physics-informed DEM accounts for multiple vibration modes of the constituting beam elements in wide frequency ranges. We construct various DEMs mimicking cylinder chains and compare their wave dynamics with those measured in experiments to validate the proposed method. Furthermore, we construct a graded woodpile chain of slender cylinders. We experimentally and numerically investigate the frequency bandgaps of the system and demonstrate the possibility of constructing a wide bandgap by consecutively superposing multiple stop bands generated from cylinders of various lengths. This system is highly efficient in blocking propagating waves by leveraging the vibration isolation effect stemming from the local resonance of the cylinders. The proposed DEM method can be useful for investigating and designing complex vibration systems in an efficient and accurate manner. Moreover, the design approach of manipulating the frequency bandgap can be exploited for developing vibration filters and impact mitigation devices. [ABSTRACT FROM AUTHOR]

We numerically and experimentally investigate impact/blast-induced shock mitigation using a quasi-1D woodpile mechanical metamaterial consisting of slender cylindrical rods. In this system, nonlinear stress waves generated by the impact or blast are coupled with local bending vibration modes of the constituent rods. This result in an order of magnitude reduction of transmitted shock without relying on material damping. Specifically, we identify that the arrangement of the local resonances from low to high frequencies enables efficient mitigation of impact/blast energy by splitting strong incident waves into weak ones. We also observe that optimized patterns of the woodpile configurations based on genetic algorithm help making the wave energy equipartition and radiate efficiently in both temporal and spatial domains. This wave attenuation mechanism based on local resonances shows a great potential for the development of nonlinear elastic metamaterials for efficient impact mitigation. [ABSTRACT FROM AUTHOR]

In the present work, we numerically and experimentally investigate the propagation of nonlinear waves in a hexagonally packed granular channel. Specifically, we assemble a simple 1-2-1 granular chain, which triggers not only normal but also tangential interactions of particles up on a striker impact. We experimentally measure the transmission of nonlinear waves propagating along the channel direction using an embedded piezoelectric sensor particle. For numerical simulations, we introduce a discrete element model that accounts for both elastic and damping effects in axial and rotational directions. As a result, we find that the wave propagation in this 1-2-1 hexagonal architecture is governed strongly by the rotational dynamics of particles. We also verify that the effect of rotational damping is crucial for the accurate description of the particle’s dynamics. The findings in this study hints the significance of particles’ rotational dynamics when stress waves propagate along hexagonally packed particle channels even in highly ordered 2D/3D granular architectures. [ABSTRACT FROM AUTHOR]

As an art of paper folding, origami has been widely explored by artists for centuries. Only in recent decades has it gained attention from mathematicians and engineers for its complex geometry and rich mechanical properties. The surge of origami-inspired metamaterials has opened a new window for designing materials and structures. Typically, to build origami structures, a sheet of material is folded according to the creaselines that are marked with compliant mechanisms. However, despite their importance in origami fabrication, such compliant mechanisms have been relatively unexplored in the setting of origami metamaterials. In this study, we explore the relationship between the design parameters of compliant mechanisms and origami mechanical properties. In particular, we employ single hinge crease and Kresling origami, representative examples of rigid and non-rigid origami units, fabricated using a double-stitch perforation compliant mechanism design. We conduct axial compression tests using different crease parameters and fit the result into the bar-hinge origami model consisting of axial and torsional springs. We extract the relationship between the spring coefficients and crease parameters using Gaussian process regression. Our result shows that the change in the crease parameter contributes significantly to each spring element in a very different manner, which suggests the fine tunability of the compliant mechanisms depending on the mode of deformation. In particular, the spring stiffness varies with the crease parameter differently for rigid and non-rigid origami, even when the same crease parameter is tuned. Furthermore, we report that the qualitative static response of the Kresling origami can be tuned between monostable and bistable, or linear and nonlinear, by only changing the crease parameter while keeping the same fold pattern geometry. We believe that our compiled result proffers a library and guidelines for choosing compliant mechanisms for the creases of origami mechanical metamaterials. [ABSTRACT FROM AUTHOR]

We assemble granular chains composed of spheres of uniform diameter in different curved configurations. We study the properties of highly nonlinear solitary waves traveling in the curved channels as a function of the curve angle and of the radius of curvature, using experiments and numerical simulations. We observe that solitary waves propagate robustly even under drastic deflection, such as $$90^{\circ }$$ and $$180^{\circ }$$ turns. When the solitary waves encounter a sharp turn with a radius of curvature as small as one spherical particle's diameter, we report the formation of secondary solitary waves resulting from the interaction with the guiding rail. We compare experimental results with numerical simulations based on a discrete element model that accounts for nonlinear and dissipative interactions between particles. This study demonstrates that granular chains are efficient wave-guides, even in complex geometrical configurations. Moreover, the findings in this study suggest that solitary waves could be used as novel information and/or energy carriers. [ABSTRACT FROM AUTHOR]

We study the stress wave propagation in curved chains of particles (granular crystals) confined by bent elastic guides. We report the frequency- and amplitude-dependent filtering of transmitted waves in relation to various impact conditions and geometrical configurations. The granular crystals studied consist of alternating cylindrical and spherical particles pre-compressed with variable static loads. First, we excite the granular crystals with small-amplitude, broadband perturbations using a piezoelectric actuator to generate oscillatory elastic waves. We find that the linear frequency spectrum of the transmitted waves creates pass- and stop-bands in agreement with the theoretical dispersion relation, demonstrating the frequency-dependent filtering of input excitations through the diatomic granular crystals. Next, we excite high-amplitude nonlinear pulses in the crystals using striker impacts. Experimental tests verify the formation and propagation of highly nonlinear solitary waves that exhibit amplitude-dependent attenuation. We show that the wave propagation can be easily tuned by manipulating the pre-compression imposed to the chain or by varying the initial curvature of the granular chains. We use a combined discrete element (DE) and finite element (FE) numerical model to simulate the propagation of both dispersive linear waves and compactly-supported highly nonlinear waves. We find that the tunable, frequency- and amplitude-dependent filtering of the incoming signals results from the close interplay between the granular particles and the soft elastic media. The findings in this study suggest that hybrid structures composed of granular particles and linear elastic media can be employed as new passive acoustic filtering materials that selectively transmit or mitigate excitations in a desired range of frequencies and amplitudes. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the reflection of highly nonlinear solitary waves in one-dimensional granular crystals interacting with large plates. We observe significant changes in the reflected waves’ properties in terms of wave amplitude and time of flight in association with the intrinsic inelasticity of large plates, which are governed by the plate thickness and the size of the granular constituents. We also study the effects of fixed plate boundaries in the formation of reflected waves, and find the existence of a critical distance, within which the interaction between the granular chain and plate is strongly modified. We explain the effects of intrinsic inelasticity and of boundaries in the large plates by using plate theory and the contact mechanics between a plate and a spherical striker. We find that experimental results are in excellent agreement with the analytical predictions and numerical simulations based on the combined discrete element and spectral element models. The findings in this study can be useful for the nondestructive evaluation of plate structures using granular crystals, which can improve the resolution of in-situ, portable measurement instruments leveraging high acoustic energy and sensitivity of solitary waves. [Copyright &y& Elsevier]

We study the wave propagation in a curved chain of spherical particles constrained by elastic guides under the axial impact of a falling mass. We characterize the force transmission properties of the chain by varying the striker's mass and the chain's curvature. Experimental tests demonstrate amplitude-dependent attenuation of compressive waves propagating through the curved chain. In particular, we observe that the curved systems present an improved transmission of small dynamic disturbances relative to that of strong excitations, resulting from the close interplay between the granular particles and the softer elastic medium. We also find that the transmission of the compressive waves through the chains is dependent on the initial curvature imposed to the system. Numerical simulations, based on an approach that combines discrete element and finite element methods, corroborate the experimental results. The findings suggest that hybrid structures composed of granular particles and linear elastic media can be employed as new passive acoustic filtering materials that selectively transmit or mitigate excitations in a desired range of pressure amplitudes. [ABSTRACT FROM AUTHOR]

A new strategy for monitoring the condition of adjustable speed induction machine drive systems is presented in this paper. The main concept of the new method is to use the inverter to perform off-line tests for quality assessment of the vulnerable components in the inverter, cable, and induction motor automatically whenever the motor is stopped. This new approach is suitable for monitoring system components that deteriorate gradually to failure, if the degradation is observable. Off-line test methods for monitoring the quality of the 1) dc-link aluminum electrolytic capacitor; 2) electrical connections; 3) cable and stator winding insulation; 4) stator core; and 5) rotor bar are presented along with a summary of the failure mechanism and existing test methods. It will be shown that the new strategy can be implemented with minimal hardware requirements, and that it has many advantages over existing off-line and on-line tests. An experimental study performed under simulated fault conditions for each component shows that the method provides a reliable and sensitive indication of drive system problems for reliable, efficient, and safe operation. [ABSTRACT FROM PUBLISHER]

The lifetime of the stator winding insulation is reduced when operated with pulsewidth-modulation inverters, since insulation degradation is accelerated due to increased thermal and electrical stresses on the motor. This paper focuses on a new approach for monitoring the condition of the stator insulation for failure-prone inverter-fed machines. The main concept of the proposed technique is to apply a dc and/or variable-frequency ac test voltage to the stator insulation using the inverter and to perform standard offline insulation tests whenever the motor is not operating. This allows the stator insulation to be tested more frequently as compared to offline tests performed once every three to six years during periodic maintenance. Two methods for testing the insulation with minimal modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low-cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. This does not only helps prevent forced outages and safety risks due to insulation breakdown but also helps perform maintenance in an efficient manner, since individual motor maintenance can be prioritized and scheduled based on its present condition. [ABSTRACT FROM AUTHOR]

This study investigates the mode I intra-laminar fracture and size effect in Discontinuous Fiber Composites (DFCs). Towards this goal, the results of fracture tests on geometrically-scaled Single Edge Notch Tension (SENT) specimens are presented and critically discussed for three platelet sizes. The results clearly show a decrease in nominal strength as the specimen size increases. It is found that, when the specimen is sufficiently large, the structural strength scales according to Linear Elastic Fracture Mechanics (LEFM) and the failure occurs in a very brittle way. In contrast, small specimens exhibit a more pronounced pseudo-ductility with a limited scaling effect and a significant deviation from LEFM. To characterize the fracture energy and the effective length of the fracture process zone, an approach combining equivalent fracture mechanics and stochastic finite element modeling is proposed. The model accounts for the complex random mesostructure of the material by modeling the platelets explicitly. Thanks to this theoretical framework, the mode I fracture energy of DFCs is estimated for the first time and it is shown to depend significantly on the platelet size. In particular, the fracture energy is shown to increase linearly with the platelet size in the range investigated in this work. Another importance of this work is that, compared to traditional unidirectional composites, DFC structures exhibit higher pseudo-ductility and their strength is, by far, less sensitive to notches, defects and cracks. This aspect can be used advantageously in structural design only upon the condition that proper certification guidelines acknowledging the more pronounced quasibrittleness of DFCs is formulated. The size effect analysis presented in this work represents a first step in this direction as it allows the assessment of the severity of a defect or notch in DFCs. [ABSTRACT FROM AUTHOR]

We study the Bloch oscillation of elastic waves in a chain composed of hollow elliptical cylinders (HECs). These HECs are 3D-printed in different wall thicknesses and are arranged to form a graded chain. We find that the frequency band structure of this lattice can be manipulated in a way to create a narrow strip of transmission range sandwiched between slanted stop bands. This results in the trapping of elastic waves at a specific location of the chain, which depends on the input frequency of the propagating elastic waves. This elastic Bloch oscillation in a tailorable 3D-printed system enables the control of energy localization in solids, potentially leading to engineering applications for vibration filtering, energy harvesting, and structural health monitoring. [ABSTRACT FROM AUTHOR]

Environment stress is a major threat to the existence of coral reefs and has generated a lot of interest in the coral research community. Under the environmental stress, corals can experience tissue loss and/or the breakdown of symbiosis between the cnidarian host and its symbiotic algae causing the coral tissue to appear white as the skeleton can be seen by transparency. Image analysis is a common method used to assess tissue response under the environmental stress. However, the traditional approach is limited by the dynamic nature of the coral-algae symbiosis. Here, we observed coral tissue response in the scleractinian coral, Montipora capricornis, using high frequency image analysis throughout the experiment, as opposed to the typical start/end point assessment method. Color analysis reveals that the process can be divided into five stages with two critical stages according to coral tissue morphology and color ratio. We further explore changes to the morphology of individual polyps by means of the Pearson correlation coefficient and recurrence plots, where the quasi-periodic and nonstationary dynamics can be identified. The recurrence quantification analysis also allows the comparison between the different polyps. Our research provides a detailed visual and mathematical analysis of coral tissue response to environmental stress, which potentially shows universal applicability. Moreover, our approach provides a robust quantitative advancement for improving our insight into a suite of biotic responses in the perspective of coral health evaluation and fate prediction. [ABSTRACT FROM AUTHOR]

Pre-folded tubes can exhibit superior energy absorption characteristics under axial crushing compared to conventional straight-walled tubes. However, their construction can be difficult to automate. In this investigation, we present a novel filament winding approach to efficiently manufacture pre-folded carbon fiber reinforced plastic (CFRP) tubes featuring the Kresling fold pattern. We experimentally study the quasi-static axial crushing behavior of three Kresling geometries and compare them to conventional tubes with a circular and square cross-section. The data from experiments is used to develop a finite element model for estimating axial crush indicators. Despite the layup sequence not orienting the fibers in the direction of loading, we obtain superior structural performance in terms of the mean force divided by the initial peak crushing force, which represents the crushing force efficiency of the structure. The tested tubes exhibit further potential to improve their energy absorption performances, while preserving enhanced manufacturability. [ABSTRACT FROM AUTHOR]

With the ease of gene sequencing and the technology available to study and manipulate non-model organisms, the extension of the methodological toolbox required to translate our understanding of model organisms to non-model organisms has become an urgent problem. For example, mining of large coral and their symbiont sequence data is a challenge, but also provides an opportunity for understanding functionality and evolution of these and other non-model organisms. Much more information than for any other eukaryotic species is available for humans, especially related to signal transduction and diseases. However, the coral cnidarian host and human have diverged over 700 million years ago and homologies between proteins in the two species are therefore often in the gray zone, or at least often undetectable with traditional BLAST searches. We introduce a two-stage approach to identifying putative coral homologues of human proteins. First, through remote homology detection using Hidden Markov Models, we identify candidate human homologues in the cnidarian genome. However, for many proteins, the human genome alone contains multiple family members with similar or even more divergence in sequence. In the second stage, therefore, we filter the remote homology results based on the functional and structural plausibility of each coral candidate, shortlisting the coral proteins likely to have conserved some of the functions of the human proteins. We demonstrate our approach with a pipeline for mapping membrane receptors in humans to membrane receptors in corals, with specific focus on the stony coral, P. damicornis. More than 1000 human membrane receptors mapped to 335 coral receptors, including 151 G protein coupled receptors (GPCRs). To validate specific sub-families, we chose opsin proteins, representative GPCRs that confer light sensitivity, and Toll-like receptors, representative non-GPCRs, which function in the immune response, and their ability to communicate with microorganisms. Through detailed structure-function analysis of their ligand-binding pockets and downstream signaling cascades, we selected those candidate remote homologues likely to carry out related functions in the corals. This pipeline may prove generally useful for other non-model organisms, such as to support the growing field of synthetic biology. [ABSTRACT FROM AUTHOR]

Turn insulation degradation is one of the major root causes of stator insulation failure leading to motor breakdown. The surge test is the only test available for testing the integrity of turn insulation; however, it is a high voltage pass/fail test that provides an indication only if an arc is instigated between the turns of weakened turn insulation, and therefore does not provide information regarding remaining lifetime. The surge PD test measures the partial discharge (PD) activity under surge excitation, and is used to date for assuring that voltage source PWM inverter-fed motors (IEC 60034-18-41 type I) are PDfree. In this paper, the potential of using the surge PD test as a predictive maintenance tool for turn insulation quality assessment is evaluated. Under the expectation that increasing PD activity in the voids formed by insulation degradation may be detectable before turn insulation failure, the test is performed periodically under accelerated thermal degradation on 6 windings. It is shown that change in the PD inception voltage under the surge PD test can be clearly observed before any other insulation test indicator. The results suggest that the surge PD test can be used for monitoring the condition of turn insulation for providing an early indication of stator insulation problems without the risk of puncturing turn insulation. [ABSTRACT FROM AUTHOR]

As a renewable energy harvesting method, interest in piezoelectric energy harvesting has increased significantly. Despite the piezoelectric energy-harvesting technology expanding its area to the flexible (elastic, amendable) devices, striking use or application of the technology is hardly found in the market. Here, we report a novel flexible piezoelectric energy harvester fabricated by using an additive manufacturing process, which enables both effective and customized manufacturing technique. By taking advantages of additive manufacturing, further application of the piezoelectric energy-harvesting technology is highly expected. Particles of BaTiO3, a ceramic with a large piezoelectric constant, were mixed with polyether block amide elastomer to form a flexible piezoelectric composite. The energy harvester was fabricated using an additive manufacturing process, by printing the piezoelectric composite on a laser-patterned flexible Indium-tin-oxide–coated polyethylene terephthalate substrate. Performance of fabricated energy harvester was evaluated by applying a mechanical stress to the energy harvester; voltage and current output were 2 V and 40 nA, respectively. An analytical model of the piezoelectric energy harvester was developed and discussed to explain the form of the voltage waveforms in response to the applied stress. [ABSTRACT FROM AUTHOR]

We investigated the effects of transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) with neurodevelopmental treatment (NDT) on the improvement of motor development and reduction of spasticity in children with cerebral palsy (CP). Twenty-four children with CP were allocated to two groups: the tDCS + NDT group and the only NDT group, done 3 times per week for 5 weeks. The Gross Motor Function Measurement (GMFM-88) and Box and Block Test (BBT) were used to assess changes in motor development, and the Modified Ashworth Scale (MAS) was used to evaluate changes in spasticity. All measurements were carried out at 3 time points: baseline, post-intervention, and 1 month follow-up. We found improvements in the GMFM-88 total scores and in each individual GMFM-88 dimension scores, favoring the tDCS + NDT group over the only NDT group. The BBT scores improved only in the tDCS + NDT group. In addition, the MAS scores reduced in the hemibody with significant motor impairment only in the tDCS + NDT group. The present findings suggest that tDCS combined with NDT can be considered a promising intervention for children with CP, as it can enhance motor development and reduce spasticity in this population. [ABSTRACT FROM AUTHOR]

We study the formation and propagation of nonlinear stress waves in 3D woodpile elastic metamaterials consisting of vertically stacked slender cylindrical rods. We find the nonlinear waveforms transmitted through the woodpile architectures under impact are highly sensitive to their design parameters, particularly stacking distances and angles in 3D assemblies. We numerically and experimentally demonstrate that the woodpile system can localize, modulate, and ultimately attenuate propagating nonlinear waves in an efficient manner without relying on material damping. We also show the feasibility of constructing metamaterials with a simultaneous characteristic of high damping and high stiffness by using the controllable wave dispersion in the woodpile structures. These woodpile metamaterials offer enhanced degrees of freedom in manipulating stress waves, thereby offering a new way to design efficient impact protectors with high stiffness. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a nondestructive evaluation technique based on the propagation of highly nonlinear solitary waves (HNSWs) to monitor the hydration of cement. HNSWs are mechanical waves that can form and travel in highly nonlinear systems, such as one-dimensional chains of contacting spherical particles (i.e., granular crystals). In the present study, we use a granular crystal-based actuator/sensor to observe the solitary waves propagating to and from the mechanical interface between the transducer and a fresh gypsum cement sample. We hypothesize that the reflected HNSWs traveling along the crystal-based transducer are affected by the hydration process of the cement, and we assess the elastic modulus of the specimen in the localized region of the granular crystal contact. To verify the experimental results, we perform numerical simulations based on a simplified finite element model. The elastic properties of the cement specimen measured by the granular crystal transducer are compared with the compressive strength and the elastic modulus measurements obtained from destructive tests, conducted according to the ASTM C109. We observe good agreement between experiments and numerical simulations. [Copyright &y& Elsevier]

It is difficult to apply conventional online motor current signature analysis techniques for diagnosis of rotor faults for closed-loop induction motor drives for many applications due to the masking effect of the feedback current controller and/or variable frequency or load operation. Relying solely on traditional offline inspection techniques during regular maintenance does not allow frequent monitoring of rotor problems and is inconvenient since it requires rotor disassembly and/or manual rotor rotation. In this paper, a new automated technique for testing voltage source inverter-fed squirrel-cage induction machines at a standstill for rotor faults is proposed. The main concept is to use the inverter to excite the machine with a pulsating field at a number of angular positions to observe the variation in the impedance pattern due to broken rotor bars, whenever the motor is stopped. An experimental study on a 7.5-hp induction motor verifies that broken bars can be detected with high sensitivity and reliability. It will be shown that the proposed method can provide automated and reliable assessment of rotor condition frequently without motor disassembly, manual rotation, or additional instrumentation. The proposed test can also provide rotor quality assessment independent of variations in motor or load operating conditions since it is a standstill test. [ABSTRACT FROM AUTHOR]

Model systems approaches search for commonality in patterns underlying biological diversity and complexity led by common evolutionary paths. The success of the approach does not rest on the species chosen but on the scalability of the model and methods used to develop the model and engage research. Fine-tuning approaches to improve coral cell cultures will provide a robust platform for studying symbiosis breakdown, the calcification mechanism and its disruption, protein interactions, micronutrient transport/exchange, and the toxicity of nanoparticles, among other key biological aspects, with the added advantage of minimizing the ethical conundrum of repeated testing on ecologically threatened organisms. The work presented here aimed to lay the foundation towards development of effective methods to sort and culture reef-building coral cells with the ultimate goal of obtaining immortal cell lines for the study of bleaching, disease and toxicity at the cellular and polyp levels. To achieve this objective, the team conducted a thorough review and tested the available methods (i.e. cell dissociation, isolation, sorting, attachment and proliferation). The most effective and reproducible techniques were combined to consolidate culture methods and generate uncontaminated coral cell cultures for ~7 days (10 days maximum). The tests were conducted on scleractinian corals Pocillopora acuta of the same genotype to harmonize results and reduce variation linked to genetic diversity. The development of cell separation and identification methods in conjunction with further investigations into coral cell-type specific metabolic requirements will allow us to tailor growth media for optimized monocultures as a tool for studying essential reef-building coral traits such as symbiosis, wound healing and calcification at multiple scales. [ABSTRACT FROM AUTHOR]

Coral reef ecosystems support significant biological activities and harbor huge diversity, but they are facing a severe crisis driven by anthropogenic activities and climate change. An important behavioral trait of the coral holobiont is coral motion, which may play an essential role in feeding, competition, reproduction, and thus survival and fitness. Therefore, characterizing coral behavior through motion analysis will aid our understanding of basic biological and physical coral functions. However, tissue motion in the stony scleractinian corals that contribute most to coral reef construction are subtle and may be imperceptible to both the human eye and commonly used imaging techniques. Here we propose and apply a systematic approach to quantify and visualize subtle coral motion across a series of light and dark cycles in the scleractinian coral Montipora capricornis. We use digital image correlation and optical flow techniques to quantify and characterize minute coral motions under different light conditions. In addition, as a visualization tool, motion magnification algorithm magnifies coral motions in different frequencies, which explicitly displays the distinctive dynamic modes of coral movement. Specifically, our assessment of displacement, strain, optical flow, and mode shape quantify coral motion under different light conditions, and they all show that M. capricornis exhibits more active motions at night compared to day. Our approach provides an unprecedented insight into micro-scale coral movement and behavior through macro-scale digital imaging, thus offering a useful empirical toolset for the coral research community. [ABSTRACT FROM AUTHOR]

Metamaterials are a class of engineered materials that often violate the routine assumptions that apply to ordinary materials. While metamaterials are typically assembled from carefully designed mesoscale units, the intended bulk-scale functionality can be obscured by unintended emergent effects driven by non-additive unit-unit interactions. These interactions are often sensitive to the number of units and their overall arrangement, making them extrinsic to the unit-scale design. As such, the emergence of extrinsic effects adds a significant hurdle for the development of general-purpose metamaterial technologies. Here, we reconceptualize bulk-scale extrinsic properties as a design opportunity and develop an approach that repurposes them in a new class of exponentially reconfigurable origami-inspired mechanical metamaterials. We illustrate the use of extrinsic properties to design a single general-purpose structure that can be transformed into a variety of passive mechanical devices including a waveguide, a wave lens, and a wave cloak. Bench-top experiments validate the core concepts of our approach and show how unintentional extrinsic effects become useful for applications of reconfigurable metamaterials. Unlabelled Image • Modular metamaterials are proposed with an exponentially large number of configurations. • Each unit cell can switch into 4 patterns with multiple acoustic properties. • Cellular metamaterial can be in situ set as wave filter, guide, lens and cloak. • Extrinsic effect is reconceptualized as a design opportunity to form reconfigurable metamaterials. [ABSTRACT FROM AUTHOR]

We investigate the reconfigurability and tunability of the tessellation of Tachi-Miura Polyhedron (TMP), an origami-based cellular structure composed of bellows-like unit cells. Lattice-based three-dimensional mechanical metamaterials have recently received significant scientific interest due to their superior and unique mechanical performance compared to conventional materials. However, it is often challenging to achieve tunability and reconfigurability from these metamaterials, since their geometry and functionality tend to be pre-determined in the design and fabrication stage. Here, we utilize TMP's highly versatile phase-transforming and tessellating capabilities to design reconfigurable metamaterial architecture with tunable mechanical properties. The theoretical analyses and experiments with heat processing discover the wide range of the in-situ tunability of the metamaterial – specifically orders of magnitude change in effective density, Young's modulus, and Poisson's ratio – after its fabrication within the elastic deformation regime. We also witness a rather unique behavior of the inverse correlation between effective density and stiffness. This mechanical platform paves the way to design the metamaterial that can actively adapt to various external environments. • A post-fabrication tuning method for origami-based mechanical metamaterials is demonstrated. • A tessellation of Tachi-Miura Polyhedron is manufactured with an efficient method inspired by honeycomb structures. • Heat-processing method is leveraged to achieve the post-fabrication tuning, accompanied by theoretical analyses. • The result shows the wide range of in-situ tunability in effective density, Young's modulus, and Poisson's ratio. [ABSTRACT FROM AUTHOR]

We studied effects of material anisotropy on impact mitigation in single column woodpile structures. Local vibrations and nonlinear contacts of cylindrical members are key mechanisms of wave modulation in woodpile structures. We numerically obtained wave propagations in single column woodpile structures by changing longitudinal and/or transverse stiffness different from stiffness along the stacking direction. We found that changes in longitudinal and/or transverse stiffness altered wave propagation tendency as well as impact mitigation rate. We observed compact and wide waves propagated through single column woodpile structures with small stiffness ratio, while disintegrated but narrow waves with large stiffness ratio. According to dynamic behavior under impact loadings and frequency responses of woodpiles, bending vibration changed from 3rd to 1st mode and low energy band moved to relatively low frequency region when the single column woodpile structures had small stiffness ratio. This leads to increase impact mitigation characteristics of single column woodpile structures. [ABSTRACT FROM AUTHOR]

Nanostructured composites built with microporous cellulose fibers and carbon nanotubes (CNTs) have potential impacts in the fields of energy storage, sensors, and flexible electronics. Few results have been shown for high mechanoelectrical sensitivity of CNT‐paper composite because of numerous current paths in the network. Here, CNT‐paper‐based nanostructured composite sensors whose sensitivities are generated by controlled tensile fracture of the composite are presented. Under uniaxial load, the cellulose fibers in the paper experience straightening, stiffening, and fracture. The cellulose fibers originally parallel to the tension are fractured while those inclined and perpendicular to the tension are reorganized to form crossbar junctions in the vicinity of a crack. The cross junctions exhibit resistive and capacitive sensitivity to the out‐of‐plane force by the compression of the junctions. Such piezoresistive and piezocapacitive sensitivities are characterized and evaluated for human behavior monitoring. [ABSTRACT FROM AUTHOR]

In this paper, we present a review of machine health managements for the smart factory. As the Industry 4.0 leads current factory automation and intelligent machines, the machine health management for diagnostic and prognostic purposes are essential, and their importance is getting more significant for the realization of the smart factory in the Industry 4.0. After brief introductions to important concepts and definitions composing smart factory and Industry 4.0, the developments in maintenance strategies towards Prognostics and health management (PHM) of machines are summarized. The review of machine health managements is followed, classifying the references by the monitoring components, types of measurements, as well as PHM tools and algorithms. 94 existing articles are reviewed and summarized in this regard. The implementations of machine health managements within the smart factory are discussed in terms of data connectivity, communications, Cyber-physical system (CPS) and virtual factory, relating them to Internet of things (IoT), cloud computing, and big data management. [ABSTRACT FROM AUTHOR]

We report the numerical and experimental study of elastic Wannier-Stark ladders and Bloch oscillations in a tunable one-dimensional granular chain consisting of cylindrical particles. The Wannier-Stark ladders are obtained by tuning the contact angles to introduce a gradient in the contact stiffness along the granular chain. These ladders manifest as resonant modes localized in the space. When excited at the corresponding resonant frequencies, we demonstrate the existence of time-resolved Bloch oscillations. The direct velocity measurements using laser Doppler vibrometry agree well with the numerical simulation results. We also show the possibility of further tailoring these Bloch oscillations by numerical simulations. Such tunable systems could be useful for applications involving the spatial localization of elastic energy. [ABSTRACT FROM AUTHOR]

We investigate the tunable characteristics of mechanical waves propagating in quasi-1D phononic crystals composed of horizontally stacked short cylinders at various contact angles and offsets. According to the Hertzian contact theory, elastic compression of laterally-touching cylindrical bodies exhibits a various range of contact stiffness depending on their alignment angles. In this study, we first assemble cylindrical particles in various combinations of inclination angles and systematically examine their forming mechanisms of frequency bandgaps. We also investigate the effect of the rattling motions of cylindrical particles by introducing asymmetric center-of-mass offsets with respect to their contact points. We find that the frequency responses of these quasi-1D phononic crystals evolve into multiple band structures as we employ higher deviations of contact angles and offsets. We calculate the dispersive behavior of propagating waves using a discrete particle model for simple zero-offset cases, while we use a finite element method for simulating the rattling motions of particles under non-zero offsets. We report branching behavior of frequency band structures and the evolution of their vibration modes as we manipulate the contact angles and offsets of the phononic crystals. This study implies that we can leverage the versatile wave filtering characteristics of quasi-1D phononic crystals to construct tunable wave filtering devices for engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A graph-based method is proposed to assess reconfigurability in origami metamaterial. • Tachi-Miura Polyhedron tessellations have an abundance of reconfigurability. • The heterogeneity and connectivity of unit cells contribute to reconfigurability. • This method contributes to designing origam metamaterial with tailored properties. Origami-based mechanical metamaterials have recently received significant scientific interest due to their versatile and reconfigurable architectures. However, it is often challenging to account for all possible geometrical configurations of the origami assembly when each origami cell can take multiple phases. Here, we investigate the reconfigurability of a tessellation of origami-based cellular structures composed of bellows-like unit cells, specifically Tachi-Miura Polyhedron (TMP). One of the unique features of the TMP is that a single cell can take four different phases in a rigid foldable manner. Therefore, the TMP tessellation can achieve various shapes out of one original assembly. To assess the geometrical validity of the astronomical number of origami phase combinations, we build a graph-theoretic framework to describe the connectivity of unit cells and to analyze the reconfigurability of the tessellations. Our approach can pave the way to develop a systematic computational tool to design origami-based mechanical metamaterials with tailored properties. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) fibers can act not only as a load-bearing component, but also as a piezoresistive and microwave lossy material when embedded in fiber-reinforced polymer composites. By leveraging these multifunctional characteristics, we propose simultaneous self-sensing and microwave-absorbing composite structures based on embedded SiC fiber networks. A SiC fiber network consists of SiC fiber yarns embedded in each interlaminar of the host composite at regular intervals. The SiC fiber yarns, which do not come into contact with other SiC fiber yarns, act as independent sensing elements using their piezoresistivity. By positioning the SiC fiber yarns at regular intervals within the wavelength of the targeted microwave-absorption bandwidth, the SiC fiber network functions as a microwave lossy material. In this study, specific focus has been placed on designing a multi-functional composite that senses external impacts and also absorbs microwaves in the X-band (8.2–12.4 GHz). The simultaneous self-sensing and microwave-absorbing performance of the fabricated SiC-embedded composite was experimentally verified through microwave return loss measurements and dynamic signal acquisition tests. The proposed SiC fiber network-embedded composite structure has great potential for use in future aerospace structures. [ABSTRACT FROM AUTHOR]

Advances in machine learning have revolutionized capabilities in applications ranging from natural language processing to marketing to health care. Recently, machine learning techniques have also been employed to learn physics, but one of the formidable challenges is to predict complex dynamics, particularly chaos. Here, we demonstrate the efficacy of quasi-recurrent neural networks in predicting extremely chaotic behavior in multistable origami structures. While machine learning is often viewed as a "black box", we conduct hidden layer analysis to understand how the neural network can process not only periodic, but also chaotic data in an accurate manner. Our approach shows its effectiveness in characterizing and predicting chaotic dynamics in a noisy environment of vibrations without relying on a mathematical model of origami systems. Therefore, our method is fully data-driven and has the potential to be used for complex scenarios, such as the nonlinear dynamics of thin-walled structures and biological membrane systems. Predicting chaotic behaviour is challenging due to the sensitivity to initial conditions, noise, the environment, and unknown factors. Here, the authors apply quasi-recurrent neural networks to predict both periodic and chaotic dynamics of the triangulated cylindrical origami cells, and provide an analysis of the hidden units' distinctive responses. [ABSTRACT FROM AUTHOR]

Pyrotechnic separation devices have been widely used in various missions of spacecraft in order to separate the structural parts with high reliability. Although they afford advantages of cost-effectiveness and high reliability, pyrotechnic separation devices generate an intensive dynamic response called pyroshock, which can lead to fatal damage to the mounted electronic equipment. Previous studies have attempted to resolve these issues with a shock isolator. However, these studies have limitations such a possible dynamic instability in low frequency and complexity in design. In the present study, a novel design of the sandwich insert is proposed to achieve enhanced shock attenuation without a shock isolator. Static-load tests were conducted to validate the structural performance of the shock-absorbing insert. In order to observe the attenuation performance, shock propagation and response experiments were carried out with consideration that the inserts were utilized to connect parts and to mount devices on the panel. In addition, swept sine vibration tests were carried out to investigate the dynamic response in low frequency. The shock-absorbing insert reduced propagating shock for the joint structure, and the shock response of the mounted equipment was significantly attenuated. The novel shock-absorbing insert saves space and is dynamically stable, and furthermore has the ability to protect the small electronic equipment, which is mounted on the honeycomb sandwich panel, from severe shock. These advantages make it a suitable insert for space structure application for connecting parts or mounting equipment. [ABSTRACT FROM AUTHOR]

Deployable structures are typically made of thin membranes and slender elements, which often require foldable – yet stiff – mechanical properties. The use of carbon fiber reinforced polymer (CFRP) composites for such deployable structures has been limited due to the their rigid and unfoldable nature in general. Here, we design, fabricate, and demonstrate foldable – yet stiff – structures made of CFRP composites. To achieve this, we leverage origami design principles based on the Tachi-Miura-Polyhedron (TMP) architecture. To manufacture TMP structures, we devise a unique vacuum-bag-only composite fabrication method by using compliant urethane epoxies impregnated into woven glass fiber layers on which pre-made CFRP tiles are positioned. We show the resulting structures feature self-deployability, high compactness, and deterministic force–displacement characterization. Potential applications of the proposed composite origami are abundant, including deployable habitats for space exploration and disaster relief, deployable solar arrays and antennas, actively-controlled aerodynamic surfaces, and impact mitigation structures. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

In article number 1800027, Jan Wiersig, Shumin Xiao, Qinghai Song, and co‐workers demonstrate chaotic‐to‐regular tunneling through the dynamical barriers between the chaotic sea and stable islands in a mixed phase space structure. This research will shed light on the fundamental studies on quantum chaos and the practical applications in optical sensing. [ABSTRACT FROM AUTHOR]

In mixed phase space structures, the stable islands and chaotic sea are separated by dynamical barriers. Considering the small tunneling rate, intuitively, the properties of long‐lived resonances within stable islands are supposed to be less affected by the perturbations in chaotic sea. Here, the modifications on the chaotic sea which can be transported through dynamical barriers and strongly affect long‐lived resonances within stable islands are experimentally demonstrated. In waveguide‐connected quadruple microdisks (WCQMs), the finite orbital angular momentum and the propagation directions of long‐lived resonances within stable islands could be changed and controlled by the waveguides connecting to the chaotic sea. The numerical calculations and the corresponding 4 × 4 non‐Hermitian Hamiltonian theoretical model match the experimental results well and demonstrate the essential roles of asymmetrical scattering in the chaotic sea and chaotic‐to‐regular tunneling. This research will be interesting for fundamental studies on quantum chaos and practical applications in optical sensing. Systems with mixed phase space structures are fundamentally important for quantum chaos, tunneling, and their practical applications. Until now, most of research is focused on tunneling from regular states to the chaotic sea. The reversal process, chaotic‐to‐regular tunneling, is usually neglected due to its rapid leakage and small tunneling probability. Here, changes in chaotic sea are transported through dynamical barriers and strongly affect long‐lived resonances within stable islands. [ABSTRACT FROM AUTHOR]