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Origami structures have been widely used in various engineering fields due to their desirable properties such as geometric transformability and high specific energy absorption. Based on the Kresling origami pattern, this study proposes a type of thin-walled origami tube the structural configuration of which is found by a mixed-integer linear programming model. Using finite element analysis, a reasonable configuration of a thin-walled tube with the Kresling pattern is firstly analyzed. Then, the influences of different material properties, the rotation angle of the upper and lower sections of the tube unit, and cross-sectional shapes on the energy absorption behavior of the thin-walled tubes under axial compression are evaluated. The results show that the symmetric thin-walled tube with the Kresling pattern is a reasonable choice for energy absorption purposes. Compared with thin-walled prismatic tubes, the thin-walled tube with the Kresling pattern substantially reduces the initial peak force and the average crushing force, without significantly reducing its energy absorption capacity; moreover, it enters the plastic energy dissipation stage ahead of time, giving it a superior energy absorption performance. Besides, the material properties, rotation angle, and cross-sectional shape have considerable influences on its energy absorption performance. The results provide a basis for the application of the Kresling origami pattern in the design of thin-walled energy-absorbingstructures.

We have analyzed the physical mechanisms responsible for the formation of an ordered sequence of nanoclusters synthesized on a nanowire in the diffusion mode of deposition of free atoms. The result...

Conventional microfabrication processes have been well established, but their capabilities are generally limited simple and 2D extruded geometries. Additive manufacturing allows the ability to manufacture true 3D complex geometries, rapid design for manufacturing, mass customisation, materials savings, and high precision which have triggered the increased interest in manufacturing microelectromechanical systems (MEMS). This paper consolidates MEMS manufacturing's recent advancements, including both conventional and additive manufacturing technologies, their working principles, and practical capabilities. The paper also discusses in detail the use of additive manufacturing in several MEMS areas such as in microelectronics, circuitry, microfluidics, lab on a chip, packaging, and structural MEMS. Furthermore, the potentials and limitations of additive manufacturing are investigated with regards to the MEMS requirements. Finally, the technology outlook and improvements are discussed. This study showed that additive manufacturing has offered a promising future for the fabrication of microelectromechanical systems, especially using high resolution techniques such as microstereolithography, materials jetting, and materials extrusion. On the other hand, current challenges such as materials requirements, equipment innovation, fabricating of in vivo devices for biomedical applications, inherited defects and poor surface finish, adhesion to substrates, and productivity are areas that requires further study to increase the uptake by the MEMS community.

Deep cantilever beams, modeled using Timoshenko beam kinematics, have numerous applications in engineering. This study deals with the nonlinear dynamic response in a nonprismatic Timoshenko beam characterized by considering the deformed configuration of the axis. The mathematical model is derived using the extended Hamilton’s principle under the condition of finite deflections and angles of rotation. The discrete model of the beam motion is constructed based on the finite difference method (FDM), whose validity is examined by comparing the results for a special case with the corresponding data obtained by commercial finite element (FE) software abaqus 2019. The natural frequencies and vibration modes of the beam are computed. These results demonstrate decreasing eigenfrequency in the beam with increasing amplitudes of nonlinear oscillations. The numerical analyses of forced vibrations of the beam show that its points oscillate in different manners depending on their relative position along the beam. Points close to the free end of the beam are subject to almost harmonic oscillations, and the free end vibrates with a frequency equal to that of the external force. When a point approaches the clamped end of the beam, it oscillates in two-frequency mode and lags in phase from the oscillations of the free end. The analytical model allows for the study of the influence of each parameter on the eigenfrequency and the dynamic response. In all cases, a strong correlation exists between the results obtained by the analytical model and ABAQUS; nonetheless, the analytical model is computationally less expensive.

The development of multi-stable structural forms has attracted considerable attention in the design of architected multi-materials, metamaterials, and morphing structures, as a result of some unusual properties such as negative stiffness and, possibly, negative Poisson's ratio. Multi-stability is achieved through a morphological change of shape upon loading, and in doing so multi-stable structures undergo transitions from one equilibrium state to another. This paper investigates the structural performance of the negative stiffness honeycomb (NSH) metamaterials made of double curved beams which are emerging in various applications such as sensors, actuators, and lightweight impact protective structures with structural tunability and recoverability. An analytical treatment is pursued using the Euler–Lagrange theorem and the stability of the honeycomb has been studied. Based on a static analysis of the nonlinear elastic system, the developed tangent stiffness matrix and ensuing deformation curve were assessed through multiple phases of deformation. The closed-form solution was in good agreement with the numerical finite element (FE) model at different bistability ratios. It was shown that the bistability ratio had a pronounced effect on the overall response of the honeycomb and the desired negativity in the stiffness matrix could be achieved with high bistability ratios.

Introducing multi-resonator microstructure into phononic metamaterials provides more flexibility in bandgap manipulation. In this work, 3D-acoustic metamaterials of the body- and face-centered cubic lattice systems encompassing nodal isotropic multivibrators are investigated. Our main results are: (1) the number of bandgaps equals the number, n, of internal masses as each bandgap is a result of the classical analog of the quantum level-repulsion mechanism between internal and external oscillations, and (2) the upper boundary frequencies, ωupper2i, i = 1, 2, ⋯, n, of the gaps formed coincide with eigen-frequencies, ωint;i2 ≠ 0, of the isolated multivibrator, ωupper2;i = ωint; i2, and the lower boundary frequencies, ωlower2,i2, are in good agreement with estimations as ω lower , i 2 ≈ ω ^ int ; i 2 ( ω lower , i 2 ω ^ int ; i 2 ), where ω ^ int ; i 2 represent the eigen-frequencies of the multivibrator when its external shell is motionless. The morphologies of the set of dispersion surfaces, ωm2(k), m = 1, 2, …, 6, in the corresponding passbands are similar to each other and to that of the set of dispersion surfaces, ωext; m2(k), obtained through the exclusion of internal masses. Thus, the problem of analyzing the acoustic properties of the complicated system is reduced to the study of two simple sets {ωint; i2} and ω ^ int ; i 2 , along with {ωext; m2(k)}, the morphology of which depends only on the type of lattice symmetry. This splitting renders controlled phononic bandgaps formation in homogeneous multi-resonator metamaterials feasible.

With progressive advances in the synthesis, characterization, and commercialization of nanoparticles and nanomaterials, these modern engineered materials are becoming an ingredient of innovative structural materials for various applications in civil and construction engineering. In this research, MgO nanoparticles were systematically added to normal concrete samples in order to investigate the effect of these nanomaterials on the durability of the samples under freeze and thaw conditions. The compressive and tensile strengths as well as the permeability of concrete samples containing nanoparticles were measured and compared with the corresponding values of control samples without nanoparticles. The curing time of the concrete samples, the amount of nanoparticles, and the water-cement ratios (w/c) were the variables of the experiments. Moreover, data clustering and the Charged System Search (CSS) algorithm were utilized as the numerical analysis and optimization methods. The regression analysis before clustering and after clustering proved the process of clustering is a prerequisite of regression analysis. Furthermore, the CSS optimization method showed that the optimum amount of nano MgO is 1% of the weight of cement, which can increase the compressive strength of concrete by 9.12% more than plain samples over 34 days.

A kinetic Monte Carlo approach is applied to study physical mechanisms responsible for the breakup of nanowires with the diamond cubic crystal structure into a chain of nanoparticles discovered in preceding experiments on Silicon nanowires. We show that this process is based on the well-known mechanism of roughening transition, which specifically manifests itself in quasi-one-dimensional systems/nanowires with a pronounced anisotropy of the surface energy density. Depending on the temperature and orientation of the nanowire relative to its internal crystal structure, the wavelengths of substantial cross-sectional modulations exceed its initial radius by 4 to 18 times. For certain orientations, a straight nanowire at the initial stage of evolution forms a serpentine/helical structure. The scenarios of the stage of nanowire ruptures into single nanoclusters are also diverse: either each spindle-shaped region of the nanowire transforms into a separate drop (by long-wave surface perturbations), or the adjacent short-scale beads absorb each other due to the Ostwald ripening effect, which can be accompanied by the formation of long-lived many-body dumbbells. The discovered features of the dynamics of quasi-onedimensional systems expand our conceptions of the physical mechanisms involved in the breakup of nanowires (presented by Nichols and Mullins as a classical model for such instabilities) which could be useful in applications based on chains of ordered nanoparticles., Comment: 38 pages, 15 figures, 7 video

Flat-foldable origami tessellations are a rich source of inspiration in the design of transformable structures and mechanical metamaterials. Among all such tessellations, the developable double corrugation (DDC) surface, popularly known as the Miura-ori, is perhaps the most ubiquitous origami pattern in science, engineering, and architectural design. Origami artists, designers, and researchers in various fields of science and engineering have proposed a range of symmetric variations for this pattern. While designing many such derivatives is straightforward, some of them present considerable geometric or crystallographic challenges. In general, the problem of finding flat-foldable derivatives for a given origami tessellation is more challenging for less symmetric descendants. This paper studies the existence and design of the least symmetric derivative of the Miura fold pattern with minimal unit cell enlargement in the longitudinal direction. The course of this study raises a fundamental problem in the flat-foldability of quadrilateral-shaped flat sheets on fold lines through their vertices. An analytical solution to this general problem is presented along with solutions for the special cases of convex quadrilaterals. Keywords: Origami design and engineering, Symmetry, Tessellations, Flat-foldability, Conics, Cubics

Investigating dispersion surface morphology of sonic metamaterials is crucial in providing information on related phenomena as inertial coupling, acoustic transparency, polarisation, and absorption. In the present study, we look into frequency surface morphology of two-dimensional metamaterials of K3,3 and K6 topologies. The elastic structures under consideration consist of the same substratum lattice points and form a pair of sublattices with hexagonal symmetry. We show that, through introducing universal localised mass-in-mass phononic microstructures at lattice points, six single optical frequency-surfaces can be formed with required properties including negative group velocity. Splitting the frequency-surfaces is based on the classical analog of the quantum phenomenon of "energy-level repulsion", which can be achieved only through internal anisotropy of the nodes and allows us to obtain different frequency band gaps., 25 pages, 15 figures

This is the peer reviewed version of the following article:Gorshkov, V.N., Sareh, P., Tereshchuk, V.V. and Soleiman‐Fallah, A. (2019), Dynamics of Anisotropic Break‐Up in Nanowires of FCC Lattice Structure. Adv. Theory Simul., 2: 1900118., which has been published in final form at https://doi.org/10.1002/adts.201900118. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions