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15 pages, 5346 KiB

Open AccessEditor’s ChoiceArticle

GAM: General Auxetic Metamaterial with Tunable 3D Auxetic Behavior Using the Same Unit Cell Boundary Connectivity

by Ismael Ben-Yelun, Guillermo Gómez-Carano, Francisco J. San Millán, Miguel Ángel Sanz, Francisco Javier Montáns and Luis Saucedo-Mora

Materials 2023, 16(9), 3473; https://doi.org/10.3390/ma16093473 - 29 Apr 2023

Cited by 6 | Viewed by 1674

Abstract

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the [...] Read more.

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the effect, (2) coupling and combining auxetic metamaterials with non-auxetic materials due to boundary compatibility, (3) obtaining the same auxetic behavior in all directions in the transverse plane, and (4) adapting the regular geometry to the component design boundary and shape. The goal of this paper is to present a novel, recently patented tunable 3D metamaterial created to reproduce a wide spectrum of 3D auxetic and non-auxetic Poisson’s ratios and Young’s moduli. This wide range is obtained using the same basic unit cell geometry and boundary connections with neighboring cells, facilitating designs using functionally graded metamaterials as only the connectivity and position of the cell’s internal nodes are modified. Based on simple spatial triangularization, the metamaterial is easily scalable and better accommodates spatial curvatures or boundaries by changing the locations of nodes and lengths of bars. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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17 pages, 9367 KiB

Open AccessArticle

A Unit Compound Structure Design: Poisson’s Ratio Is Autonomously Adjustable from Negative to Positive

by Guanxiao Zhao and Tao Fu

Materials 2023, 16(5), 1808; https://doi.org/10.3390/ma16051808 - 22 Feb 2023

Cited by 7 | Viewed by 1585

Abstract

The shape memory polymer (SMP) is a new type of smart material that can produce a shape memory effect through the stimulation of the external environment. In this article, the viscoelastic constitutive theory of the shape memory polymer and the mechanism of the [...] Read more.

The shape memory polymer (SMP) is a new type of smart material that can produce a shape memory effect through the stimulation of the external environment. In this article, the viscoelastic constitutive theory of the shape memory polymer and the mechanism of the bidirectional memory effect of the shape memory polymer are described. A chiral poly cellular circular concave auxetic structure based on a shape memory polymer made of epoxy resin is designed. Two structural parameters, α and β, are defined, and the change rule of Poisson’s ratio under different structural parameters is verified by ABAQUS. Then, two elastic scaffolds are designed to assist a new type of cellular structure made of a shape memory polymer to autonomously adjust bidirectional memory under the stimulation of the external temperature, and two processes of bidirectional memory are simulated using ABAQUS. Finally, when a shape memory polymer structure implements the bidirectional deformation programming process, a conclusion is drawn that changing the ratio β of oblique ligament and ring radius has a better effect than changing the angle α of oblique ligament and horizontal in achieving the autonomously adjustable bidirectional memory effect of the composite structure. In summary, through the combination of the new cell and the bidirectional deformation principle, the autonomous bidirectional deformation of the new cell is achieved. The research can be used in reconfigurable structures, tuning symmetry, and chirality. The adjusted Poisson’s ratio achieved by the stimulation of the external environment can be used in active acoustic metamaterials, deployable devices, and biomedical devices. Meanwhile, this work provides a very meaningful reference for the potential application value of metamaterials. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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22 pages, 15135 KiB

Open AccessArticle

Topology Optimization for Hybrid Lattice Compliant Mechanisms with Multiple Microstructures

by Nan Wei, Hongling Ye, Weiwei Wang, Jicheng Li, Fuwei Tian and Yunkang Sui

Materials 2022, 15(20), 7321; https://doi.org/10.3390/ma15207321 - 19 Oct 2022

Cited by 2 | Viewed by 1605

Abstract

Hybrid lattice compliant mechanisms (HLCMs) composed of multiple microstructures have attracted widespread interest due to their superior compliant performance compared to the traditional solid compliant mechanisms. A novel optimization scheme for HLCMs is presented using the independent continuous mapping (ICM) method. Firstly, the [...] Read more.

Hybrid lattice compliant mechanisms (HLCMs) composed of multiple microstructures have attracted widespread interest due to their superior compliant performance compared to the traditional solid compliant mechanisms. A novel optimization scheme for HLCMs is presented using the independent continuous mapping (ICM) method. Firstly, the effective properties of multiple orthogonal and anisotropic lattice microstructures are obtained by taking advantage of homogenization theory, which are used to bridge the relationship between the macrostructure layout and microstructure recognition. Then, a new parallel topology optimization model for optimizing HLCMs is built via a generalized multi-material, recognizing interpolation scheme with filter functions. In addition, the characterization relationship between independent continuous variables and performance of different elements is established. Sensitivity analysis and linear programming are utilized to solve the optimal model. Lastly, numerical examples with a displacement inverter mechanism and compliant gripper mechanism demonstrate the effectiveness of the proposed method for designing HLCMs with various lattice microstructures. Anisotropic lattice microstructures (ALMs) significantly facilitate the efficient use of constitutive properties of materials. Hence, HLCMs consisting of various ALMs achieve superior compliant performance than counterparts comprising different orthogonal lattice microstructures (OLMs). The presented method offers a reference to optimize HLCMs, as well as promotes the theoretical development and application of the ICM method. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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26 pages, 37206 KiB

Open AccessArticle

Novel Design Scheme for Structural Fundamental Frequency of Porous Acoustic Metamaterials

by Ying Zhou, Hao Li, Mengli Ye, Yun Shi and Liang Gao

Materials 2022, 15(19), 6569; https://doi.org/10.3390/ma15196569 - 22 Sep 2022

Cited by 2 | Viewed by 1658

Abstract

Structural resonance increases the vibration and noise of porous acoustic metamaterials while reducing the energy consumption and conversion efficiency of acoustic waves. Therefore, structural fundamental frequency of porous acoustic metamaterials is required to be controlled to avoid resonance. This study proposes a full-cycle [...] Read more.

Structural resonance increases the vibration and noise of porous acoustic metamaterials while reducing the energy consumption and conversion efficiency of acoustic waves. Therefore, structural fundamental frequency of porous acoustic metamaterials is required to be controlled to avoid resonance. This study proposes a full-cycle interactive progressive (FIP) design scheme for porous acoustic metamaterials. The FIP design scheme first establishes a specific parameter relationship for the initial model based on the intentions of the designers. The initial model is then dynamically adjusted through a series of optimization processes. In particular, the FIP design scheme is developed for a porous acoustic metamaterial in an acoustic-structure interaction system. The effects of the structural parameters and applied boundary conditions of the porous acoustic metamaterial on the structural fundamental frequency are investigated. A surrogate model is introduced to reduce the calculation costs and improve the design efficiency of the parametric optimization. The frequency-modulation acoustic metamaterial is tailored to improve its acoustic and vibrational characteristics, including the resonance resistance and low dynamic response. The features of the FIP design scheme in the optimized design of porous acoustic metamaterials are demonstrated. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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18 pages, 10683 KiB

Open AccessEditor’s ChoiceArticle

Design and Manufacturing of a Metal-Based Mechanical Metamaterial with Tunable Damping Properties

by Konstantin Kappe, Jan P. Wahl, Florian Gutmann, Silviya M. Boyadzhieva, Klaus Hoschke and Sarah C. L. Fischer

Materials 2022, 15(16), 5644; https://doi.org/10.3390/ma15165644 - 17 Aug 2022

Cited by 6 | Viewed by 2485

Abstract

In the present work, a novel concept for metallic metamaterials is presented, motivated by the creation of next-generation reversible damping systems that can be exposed to various environmental conditions. For this purpose, a unit cell is designed that consists of a parallel arrangement [...] Read more.

In the present work, a novel concept for metallic metamaterials is presented, motivated by the creation of next-generation reversible damping systems that can be exposed to various environmental conditions. For this purpose, a unit cell is designed that consists of a parallel arrangement of a spring and snap-fit mechanism. The combination of the two concepts enables damping properties one order of magnitude higher than those of the constituting metal material. The spring element stores elastic energy while the snap-fit allows to absorb and dissipate energy and to reach a second stable state. Different configurations of single unit cells and connected cell assemblies are manufactured by laser powder bed fusion using Ti6Al4V powder. The dimensioning is supported by finite element modelling and the characteristic properties of the unit cells are studied in cyclic compression experiments. The metamaterial exhibits damping properties in the range of polymeric foams while retaining its higher environmental resistance. By variation of selected geometrical parameters, either bistable or self-recovering characteristics are achieved. Therefore, a metamaterial as an assembly of the described unit cells could offer a high potential as a structural element in future damping or energy storage systems operating at elevated temperatures and extreme environmental conditions. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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23 pages, 19384 KiB

Open AccessArticle

A Hybrid Level Set Method for the Topology Optimization of Functionally Graded Structures

by Junjian Fu, Zhengtao Shu, Liang Gao and Xiangman Zhou

Materials 2022, 15(13), 4483; https://doi.org/10.3390/ma15134483 - 25 Jun 2022

Cited by 3 | Viewed by 1796

Abstract

This paper presents a hybrid level set method (HLSM) to design novelty functionally graded structures (FGSs) with complex macroscopic graded patterns. The hybrid level set function (HLSF) is constructed to parametrically model the macro unit cells by introducing the affine concept of convex [...] Read more.

This paper presents a hybrid level set method (HLSM) to design novelty functionally graded structures (FGSs) with complex macroscopic graded patterns. The hybrid level set function (HLSF) is constructed to parametrically model the macro unit cells by introducing the affine concept of convex optimization theory. The global weight coefficients on macro unit cell nodes and the local weight coefficients within the macro unit cell are defined as master and slave design variables, respectively. The local design variables are interpolated by the global design variables to guarantee the C⁰ continuity of neighboring unit cells. A HLSM-based topology optimization model for the FGSs is established to maximize structural stiffness. The optimization model is solved by the optimality criteria (OC) algorithm. Two typical FGSs design problems are investigated, including thin-walled stiffened structures (TWSSs) and functionally graded cellular structures (FGCSs). In addition, additively manufactured FGCSs with different core layers are tested for bending performance. Numerical examples show that the HLSM is effective for designing FGSs like TWSSs and FGCSs. The bending tests prove that FGSs designed using HLSM are have a high performance. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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15 pages, 12925 KiB

Open AccessEditor’s ChoiceArticle

Topology Optimization of Piezoelectric Energy Harvesters for Enhanced Open-Circuit Voltage Subjected to Harmonic Excitations

by Meng He, Mu He, Xiaopeng Zhang and Liang Xia

Materials 2022, 15(13), 4423; https://doi.org/10.3390/ma15134423 - 22 Jun 2022

Cited by 3 | Viewed by 2045

Abstract

Energy harvesting devices made of piezoelectric material are highly anticipated energy sources for power wireless sensors. Tremendous efforts have been made to improve the performance of piezoelectric energy harvesters (PEHs). Noticeably, topology optimization has shown an attractive potential to design PEHs with enhanced [...] Read more.

Energy harvesting devices made of piezoelectric material are highly anticipated energy sources for power wireless sensors. Tremendous efforts have been made to improve the performance of piezoelectric energy harvesters (PEHs). Noticeably, topology optimization has shown an attractive potential to design PEHs with enhanced energy conversion efficiency. In this work, an alternative yet more practical design objective was considered, where the open-circuit voltage of PEHs is enhanced by topologically optimizing the through-thickness piezoelectric material distribution of plate-type PEHs subjected to harmonic excitations. Compared to the conventional efficiency-enhanced designs, the open-circuit voltage of PEHs can be evidently enhanced by the proposed method while with negligible sacrifice on the energy conversion efficiency. Numerical investigations show that the voltage cancellation effect due to inconsistent voltage phases can be effectively ameliorated by optimally distributed piezoelectric materials. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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20 pages, 9421 KiB

Open AccessEditor’s ChoiceArticle

A Modified Three-Dimensional Negative-Poisson-Ratio Metal Metamaterial Lattice Structure

by Fangyi Li, Qiang Zhang, Huimin Shi and Zheng Liu

Materials 2022, 15(11), 3752; https://doi.org/10.3390/ma15113752 - 24 May 2022

Cited by 9 | Viewed by 2654

Abstract

Mechanical metamaterials are of interest to researchers because of their unique mechanical properties, including a negative Poisson structure. Here, we study a three-dimensional (3D) negative-Poisson-ratio (NPR) metal metamaterial lattice structure by adding a star structure to the traditional 3D concave structure, thus designing [...] Read more.

Mechanical metamaterials are of interest to researchers because of their unique mechanical properties, including a negative Poisson structure. Here, we study a three-dimensional (3D) negative-Poisson-ratio (NPR) metal metamaterial lattice structure by adding a star structure to the traditional 3D concave structure, thus designing three different angles with a modified NPR structure and control structure. We further study the mechanical properties via finite element numerical simulations and show that the stability and stiffness of the modified structures are improved relative to the control structure; the stability decreases with increasing star body angle. The star angle has the best relative energy absorption effect at 70.9°. The experimental model is made by selective laser melting (SLM) technology (3D printing), and the compression experiment verification used an MTS universal compressor. The experimental results are consistent with the changing trend in finite element simulation. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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11 pages, 3498 KiB

Open AccessArticle

Valley Hall Elastic Edge States in Locally Resonant Metamaterials

by Wenbo Fang, Chunyu Han, Yuyang Chen and Yijie Liu

Materials 2022, 15(4), 1491; https://doi.org/10.3390/ma15041491 - 17 Feb 2022

Cited by 10 | Viewed by 2431

Abstract

This paper presents a locally resonant metamaterial periodically rearranged as a local resonator, that is hexagonal holes arranged in a thin plate replace the elastic local resonator to achieve the quantum valley Hall effect. Due to the

C_{3 v}

symmetry in the [...] Read more.

This paper presents a locally resonant metamaterial periodically rearranged as a local resonator, that is hexagonal holes arranged in a thin plate replace the elastic local resonator to achieve the quantum valley Hall effect. Due to the

C_{3 v}

symmetry in the primitive hexagonal lattice, one Dirac point emerges at high symmetry points in the Brillouin zone in the sub-wavelength area. Rotating the beam element of the resonator can break the spatial inversion symmetry to lift the Dirac degeneracy and form a new bandgap. Thus, the band inversion is discovered by computing the relationship between the associated bandgap and the rotational parameter. We also confirmed this result by analyzing the vortex chirality and calculating the Chern number. We can discover two kinds of edge states in the projected band obtained by computing the supercell composed of different topological microstructures. Finally, the propagation behavior in various heterostructures at low frequencies was analyzed. It is shown that these valley Hall elastic insulators can guide elastic waves along sharp interfaces and are immune to backscattering from defects or disorder. By utilizing elastic resonators, a simple reconfigurable topological elastic metamaterial is realized in the sub-wavelength area. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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14 pages, 4399 KiB

Open AccessArticle

Development of a True-Biaxial Split Hopkinson Pressure Bar Device and Its Application

by Shumeng Pang, Weijun Tao, Yingjing Liang, Shi Huan, Yijie Liu and Jiangping Chen

Materials 2021, 14(23), 7298; https://doi.org/10.3390/ma14237298 - 29 Nov 2021

Cited by 3 | Viewed by 1852

Abstract

Although highly desirable, the experimental technology of the dynamic mechanical properties of materials under multiaxial impact loading is rarely explored. In this study, a true-biaxial split Hopkinson pressure bar device is developed to achieve the biaxial synchronous impact loading of a specimen. A [...] Read more.

Although highly desirable, the experimental technology of the dynamic mechanical properties of materials under multiaxial impact loading is rarely explored. In this study, a true-biaxial split Hopkinson pressure bar device is developed to achieve the biaxial synchronous impact loading of a specimen. A symmetrical wedge-shaped, dual-wave bar is designed to decompose a single stress wave into two independent and symmetric stress waves that eventually form an orthogonal system and load the specimen synchronously. Furthermore, a combination of ground gaskets and lubricant is employed to eliminate the shear stress wave and separate the coupling of the shear and axial stress waves propagating in bars. Some confirmatory and applied tests are carried out, and the results show not only the feasibility of this modified device but also the dynamic mechanical characteristics of specimens under biaxial impact loading. This novel technique is readily implementable and also has good application potential in material mechanics testing. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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17 pages, 6478 KiB

Open AccessArticle

Revealing the Dynamic Characteristics of Composite Material-Based Miura-Origami Tube

by Houyao Zhu, Zhixin Li, Ruikun Wang, Shouyan Chen, Chunliang Zhang and Fangyi Li

Materials 2021, 14(21), 6374; https://doi.org/10.3390/ma14216374 - 25 Oct 2021

Cited by 4 | Viewed by 2410

Abstract

Although Miura origami has excellent planar expansion characteristics and good mechanical properties, its congenital flaws, e.g., open sections leading to weak out-of-plane stiffness and constituting the homogenization of the material, and resulting in limited design freedom, should also be taken seriously. Herein, two [...] Read more.

Although Miura origami has excellent planar expansion characteristics and good mechanical properties, its congenital flaws, e.g., open sections leading to weak out-of-plane stiffness and constituting the homogenization of the material, and resulting in limited design freedom, should also be taken seriously. Herein, two identical Miura sheets, made of carbon fiber/epoxy resin composite, were bonded to form a tubular structure with closed sections, i.e., an origami tube. Subsequently, the dynamic performances, including the nature frequency and the dynamic displacement response, of the designed origami tubes were extensively investigated through numerical simulations. The outcomes revealed that the natural frequency and corresponding dynamic displacement response of the structure can be adjusted in a larger range by varying the geometric and material parameters, which is realized by combining origami techniques and the composite structures’ characteristics. This work can provide new ideas for the design of light-weight and high-mechanical-performance structures. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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16 pages, 4482 KiB

Open AccessArticle

An Aggregation-Free Local Volume Fraction Formulation for Topological Design of Porous Structure

by Kai Long, Zhuo Chen, Chengwan Zhang, Xiaoyu Yang and Nouman Saeed

Materials 2021, 14(19), 5726; https://doi.org/10.3390/ma14195726 - 30 Sep 2021

Cited by 10 | Viewed by 1689

Abstract

Cellular structure can possess superior mechanical properties and low density simultaneously. Additive manufacturing has experienced substantial progress in the past decades, which promotes the popularity of such bone-like structure. This paper proposes a methodology on the topological design of porous structure. For the [...] Read more.

Cellular structure can possess superior mechanical properties and low density simultaneously. Additive manufacturing has experienced substantial progress in the past decades, which promotes the popularity of such bone-like structure. This paper proposes a methodology on the topological design of porous structure. For the typical technologies such as the p-norm aggregation and implicit porosity control, the violation of the maximum local volume constraint is inevitable. To this end, the primary optimization problem with bounds of local volume constraints is transformed into unconstrained programming by setting up a sequence of minimization sub-problems in terms of the augmented Lagrangian method. The approximation and algorithm using the concept of moving asymptotes is employed as the optimizer. Several numerical tests are provided to illustrate the effectiveness of the proposed approach in comparison with existing approaches. The effects of the global and local volume percentage, influence radius and mesh discretization on the final designs are investigated. In comparison to existing methods, the proposed method is capable of accurately limiting the upper bound of global and local volume fractions, which opens up new possibilities for additive manufacturing. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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21 pages, 7592 KiB

Open AccessArticle

A Novel Design Method for Energy Absorption Property of Chiral Mechanical Metamaterials

by Mengli Ye, Liang Gao, Fuyu Wang and Hao Li

Materials 2021, 14(18), 5386; https://doi.org/10.3390/ma14185386 - 17 Sep 2021

Cited by 13 | Viewed by 2864

Abstract

In this paper, a full-cycle interactive progressive (FIP) method that integrates topology optimization, parametric optimization, and experimental analysis to determine the optimal energy absorption properties in the design of chiral mechanical metamaterials is proposed. The FIP method has improved ability and efficiency compared [...] Read more.

In this paper, a full-cycle interactive progressive (FIP) method that integrates topology optimization, parametric optimization, and experimental analysis to determine the optimal energy absorption properties in the design of chiral mechanical metamaterials is proposed. The FIP method has improved ability and efficiency compared with traditional design methods due to strengthening the overall design, introducing surrogate models, and its consideration of the application conditions. Here, the FIP design was applied in the design of mechanical metamaterials with optimized energy absorption properties, and a chiral mechanical metamaterial with good energy absorption and impact resistance was obtained based on the rotation mechanism of metamaterials with a negative Poisson’s ratio. The relationship among the size parameters, applied boundary conditions, and energy absorption properties were studied. An impact compression experiment using a self-made Fiber Bragg Grating sensor was carried out on the chiral mechanical metamaterial. In light of the large deviation of the experimental and simulation data, a feedback adjustment was carried out by adjusting the structural parameters to further improve the mechanical properties of the chiral mechanical metamaterial. Finally, human–computer interaction, self-innovation, and a breakthrough in the design limits of the optimized model were achieved. The results illustrate the effectiveness of the FIP design method in improving the energy absorption properties in the design of chiral mechanical metamaterials. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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19 pages, 996 KiB

Open AccessArticle

Phononic Bandgap Optimization in Sandwich Panels Using Cellular Truss Cores

by Leonel Quinteros, Viviana Meruane, Eduardo Lenz Cardoso and Rafael O. Ruiz

Materials 2021, 14(18), 5236; https://doi.org/10.3390/ma14185236 - 11 Sep 2021

Cited by 9 | Viewed by 2871

Abstract

The development of custom cellular materials has been driven by recent advances in additive manufacturing and structural topological optimization. These contemporary materials with complex topologies have better structural efficiency than traditional materials. Particularly, truss-like cellular structures exhibit considerable potential for application in lightweight [...] Read more.

The development of custom cellular materials has been driven by recent advances in additive manufacturing and structural topological optimization. These contemporary materials with complex topologies have better structural efficiency than traditional materials. Particularly, truss-like cellular structures exhibit considerable potential for application in lightweight structures owing to their excellent strength-to-mass ratio. Along with being light, these materials can exhibit unprecedented vibration properties, such as the phononic bandgap, which prohibits the propagation of mechanical waves over certain frequency ranges. Consequently, they have been extensively investigated over the last few years, being the cores for sandwich panels among the most important potential applications of lattice-based cellular structures. This study aims to develop a methodology for optimizing the topology of sandwich panels using cellular truss cores for bandgap maximization. In particular, a methodology is developed for designing lightweight composite panels with vibration absorption properties, which would bring significant benefits in applications such as satellites, spacecraft, aircraft, ships, automobiles, etc. The phononic bandgap of a periodic sandwich structure with a square core topology is maximized by varying the material and the geometrical properties of the core under different configurations. The proposed optimization methodology considers smooth approximations of the objective function to avoid non-differentiability problems and implements an optimization approach based on the globally convergent method of moving asymptotes. The results show that it is feasible to design a sandwich panel using a cellular core with large phononic bandgaps. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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Review

Jump to: Research

18 pages, 5022 KiB

Open AccessEditor’s ChoiceReview

Programming Soft Shape-Morphing Systems by Harnessing Strain Mismatch and Snap-Through Bistability: A Review

by Yi Wu, Gang Guo, Zhuxuan Wei and Jin Qian

Materials 2022, 15(7), 2397; https://doi.org/10.3390/ma15072397 - 24 Mar 2022

Cited by 3 | Viewed by 3524

Abstract

Multi-modal and controllable shape-morphing constitutes the cornerstone of the functionalization of soft actuators/robots. Involving heterogeneity through material layout is a widely used strategy to generate internal mismatches in active morphing structures. Once triggered by external stimuli, the entire structure undergoes cooperative deformation by [...] Read more.

Multi-modal and controllable shape-morphing constitutes the cornerstone of the functionalization of soft actuators/robots. Involving heterogeneity through material layout is a widely used strategy to generate internal mismatches in active morphing structures. Once triggered by external stimuli, the entire structure undergoes cooperative deformation by minimizing the potential energy. However, the intrinsic limitation of soft materials emerges when it comes to applications such as soft actuators or load-bearing structures that require fast response and large output force. Many researchers have explored the use of the structural principle of snap-through bistability as the morphing mechanisms. Bistable or multi-stable mechanical systems possess more than one local energy minimum and are capable of resting in any of these equilibrium states without external forces. The snap-through motion could overcome energy barriers to switch among these stable or metastable states with dramatically distinct geometries. Attributed to the energy storage and release mechanism, such snap-through transition is quite highly efficient, accompanied by fast response speed, large displacement magnitude, high manipulation strength, and moderate driving force. For example, the shape-morphing timescale of conventional hydrogel systems is usually tens of minutes, while the activation time of hydrogel actuators using the elastic snapping instability strategy can be reduced to below 1 s. By rationally embedding stimuli-responsive inclusions to offer the required trigger energy, various controllable snap-through actuations could be achieved. This review summarizes the current shape-morphing programming strategies based on mismatch strain induced by material heterogeneity, with emphasis on how to leverage snap-through bistability to broaden the applications of the shape-morphing structures in soft robotics and mechanical metamaterials. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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