Готові списки джерел за темами / Non-auxetic

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Добірка наукової літератури з теми "Non-auxetic"

Автор: Grafiati

Опубліковано: 9 вересня 2022

Оновлено: 18 вересня 2022

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Статті в журналах з теми "Non-auxetic"

de Jonge, Christa, Helena Kolken, and Amir Zadpoor. "Non-Auxetic Mechanical Metamaterials." Materials 12, no. 4 (February 20, 2019): 635. http://dx.doi.org/10.3390/ma12040635.

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The concept of “mechanical metamaterials” has become increasingly popular, since their macro-scale characteristics can be designed to exhibit unusual combinations of mechanical properties on the micro-scale. The advances in additive manufacturing (AM, three-dimensional printing) techniques have boosted the fabrication of these mechanical metamaterials by facilitating a precise control over their micro-architecture. Although mechanical metamaterials with negative Poisson’s ratios (i.e., auxetic metamaterials) have received much attention before and have been reviewed multiple times, no comparable review exists for architected materials with positive Poisson’s ratios. Therefore, this review will focus on the topology-property relationships of non-auxetic mechanical metamaterials in general and five topological designs in particular. These include the designs based on the diamond, cube, truncated cube, rhombic dodecahedron, and the truncated cuboctahedron unit cells. We reviewed the mechanical properties and fatigue behavior of these architected materials, while considering the effects of other factors such as those of the AM process. In addition, we systematically analyzed the experimental, computational, and analytical data and solutions available in the literature for the titanium alloy Ti-6Al-4V. Compression dominated lattices, such as the (truncated) cube, showed the highest mechanical properties. All of the proposed unit cells showed a normalized fatigue strength below that of solid titanium (i.e., 40% of the yield stress), in the range of 12–36% of their yield stress. The unit cells discussed in this review could potentially be applied in bone-mimicking porous structures.

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El Dhaba, A. R., and M. Shaat. "Modeling deformation of auxetic and non-auxetic polymer gels." Applied Mathematical Modelling 74 (October 2019): 320–36. http://dx.doi.org/10.1016/j.apm.2019.04.050.

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Hu, L. L., M. Zh Zhou, and H. Deng. "Dynamic indentation of auxetic and non-auxetic honeycombs under large deformation." Composite Structures 207 (January 2019): 323–30. http://dx.doi.org/10.1016/j.compstruct.2018.09.066.

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Mir, Mariam, Murtaza Najabat Ali, Javaria Sami, and Umar Ansari. "Review of Mechanics and Applications of Auxetic Structures." Advances in Materials Science and Engineering 2014 (2014): 1–17. http://dx.doi.org/10.1155/2014/753496.

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Анотація:

One of the important mechanical properties of materials is Poisson’s ratio, which is positive for most of the materials. However, certain materials exhibit “auxetic” properties; that is, they have a negative Poisson’s ratio. Thus auxetic and non-auxetic materials exhibit different deformation mechanisms. A specific microscopic structure in the auxetic materials is important for maintaining a negative Poisson’s ratio. Based on their distinct nature auxetic materials execute certain unique properties in contrast to other materials, which are reviewed in this paper. Thus auxetic materials have important applications in the biomedical field which are also a part of this review article. Many auxetic materials have been discovered, fabricated, and synthesized which differ on the basis of structure, scale and deformation mechanism. The different types of auxetic materials such as auxetic cellular solids, microscopic auxetic polymers, molecular auxetic materials, and auxetic composites have been reviewed comprehensively in this paper. Modeling of auxetic structures is of considerable importance and needs appropriate stress strain configurations; thus different aspects of auxetic modeling have also been reviewed. Packing parameters and relative densities are of prime importance in this regard. This review would thus help the researchers in determining and deciding the various aspects of auxetic nature for their products.

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Zulifqar, Adeel, Tao Hua, and Hong Hu. "Development of uni-stretch woven fabrics with zero and negative Poisson’s ratio." Textile Research Journal 88, no. 18 (June 17, 2017): 2076–92. http://dx.doi.org/10.1177/0040517517715095.

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Fabrics with zero or negative Poisson’s ratio are referred as auxetic fabrics, which have the unusual property of lateral expansion or zero expansion upon stretch. The use of conventional materials and machinery to produce auxetic fabrics has gained the interest of researchers in recent years. However, this approach is limited to knitted fabrics only. The development of auxetic fabric using conventional yarns and weaving technology is a research area that is still unaddressed. This paper reports a study on the development of a novel class of stretchable auxetic woven fabrics by using conventional yarns and weaving machinery. The phenomenon of differential shrinkage was successfully employed to realize auxetic geometries capable of inducing auxetic behavior in woven fabrics, and a series of auxetic woven fabrics were fabricated with elastic and non-elastic yarns and a dobby machine. The uni-axial tensile tests showed that auxetic woven fabrics developed exhibited zero or negative Poisson’s ratio over a wide range of longitudinal strain.

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Kasal, Ali, Tolga Kuşkun, and Jerzy Smardzewski. "Experimental and Numerical Study on Withdrawal Strength of Different Types of Auxetic Dowels for Furniture Joints." Materials 13, no. 19 (September 24, 2020): 4252. http://dx.doi.org/10.3390/ma13194252.

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Studies on the application of auxetic metamaterials and structures in furniture joints are very limited. However, they have huge potential for use in ready-to-assemble furniture. This study aimed to design and produce different types of auxetic dowels in 3D printing technology, and experimentally and numerically analyze the withdrawal strength of these dowels. In the scope of the study, 24 auxetic dowels with different types and size of inclusions, different diameter of holes, and a non-auxetic reference dowel were designed and produced with appropriate muffs. Dowels were 3D printed from polyamide (PA12). Poisson’s ratios, withdrawal strength, contact pressures, and friction coefficients of dowels were determined theoretically by means of numerical analyses and real static compression tests. After the pre-production of dowels, the dowels with triangular inclusions have not been found to have sufficient strength and stiffness. Withdrawal strength of dowels decreased as the size of inclusions is decreased, or dowel hole diameter is increased. Furthermore, contact pressures and stresses in auxetic dowels were considerably lower than non-auxetic dowels under the withdrawal force.

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Rapaka, Sri Datta, Manoj Pandey, and Ratna Kumar Annabattula. "Dynamic compressive behaviour of auxetic and non-auxetic hexagonal honeycombs with entrapped gas." International Journal of Impact Engineering 146 (December 2020): 103718. http://dx.doi.org/10.1016/j.ijimpeng.2020.103718.

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Xue, Yingying, Peixin Gao, Li Zhou, and Fusheng Han. "An Enhanced Three-Dimensional Auxetic Lattice Structure with Improved Property." Materials 13, no. 4 (February 24, 2020): 1008. http://dx.doi.org/10.3390/ma13041008.

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In order to enhance the mechanical property of auxetic lattice structures, a new enhanced auxetic lattice structure was designed by embedding narrow struts into a three-dimensional (3D) re-entrant lattice structure. A series of enhanced lattice structures with varied parameters were fabricated by 3D printing combined with the molten metal infiltration technique. Based on the method, parameter studies were performed. The enhanced auxetic lattice structure was found to exhibit superior mechanical behaviors compared to the 3D re-entrant lattice structure. An interesting phenomenon showed that increasing the diameter of connecting struts led to less auxetic and non-auxetic structures. Moreover, the compressive property of the enhanced structure also exhibited obvious dependence on the base material and compression directions. The present study can provide useful information for the design, fabrication and application of new auxetic structures with enhanced properties.

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Sakai, Yusuke, and Makoto Ohsaki. "Parametric Study of Non-periodic and Hybrid Auxetic Bending-Active Gridshells." Journal of the International Association for Shell and Spatial Structures 61, no. 4 (December 1, 2020): 275–84. http://dx.doi.org/10.20898/j.iass.2020.010.

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This paper presents a design method of Auxetic Bending-Active Gridshells (ABAGs), which are curved surfaces generated from the initial flat grid with 2-dimensional auxetic patterns. One of the mechanical properties of ABAGs is that a dome-like shape of a curved surface can be easily obtained by bending a grid due to negative Poisson's ratio for in-plane deformation. Shapes of auxetic patterns are relevant to Poisson's ratio. Non-periodic and/or hybrid 2-dimensional auxetic patterns are developed for designing the initial flat grid of ABAGs. Shape parameters are the sizes of each plane unit for tuning its reentrant pattern, and two types of reentrant shapes are mixed on an initial flat grid. Using the non-uniform patterns, we can obtain an asymmetric and more complex free-form surface of ABAGs than those composed of a uniform reentrant pattern. Discrete Gaussian curvature at each node on a curved surface is computed for quantitatively evaluating the properties of shapes of the obtained surfaces. Possibility of ABAGs as a new design tool is demonstrated by showing that various shapes are generated through large deformation analysis with the forced displacements at the supports.

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Ferreiro-Vila, Elias, Lucia Iglesias, Irene Lucas del Pozo, Noa Varela-Dominguez, Cong Tinh Bui, Beatriz Rivas-Murias, Jose M. Vila-Fungueiriño, et al. "Apparent auxetic to non-auxetic crossover driven by Co2+ redistribution in CoFe2O4 thin films." APL Materials 7, no. 3 (March 2019): 031109. http://dx.doi.org/10.1063/1.5087559.

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Дисертації з теми "Non-auxetic"

Pyskir, Adrien. "Application de métamatériaux aux problématiques vibroacoustiques automobiles." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEC011.

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Les métamatériaux sont des matériaux architecturés de telle sorte qu’ils présentent des propriétés exotiques, issues non pas du matériau constitutif, mais de leur structure interne. Bien qu’ayant été étudiés depuis une vingtaine d’années, peu d’applications réelles ont été recensées, notamment dans le domaine industriel. Cette thèse est consacrée aux métamatériaux élastiques susceptibles de réduire les vibrations dans les véhicules automobiles. En effet, une meilleure isolation des principales sources vibratoires permettrait l’amélioration du confort vibratoire et la durée de vie des pièces mécaniques. Les résultats de calculs numériques et essais expérimentaux montrent que les métamatériaux peuvent satisfaire des contraintes contradictoires, et représentent donc des candidats intéressants pour la réalisation d’innovations industrielles. Ce type de solutions étant fondamentalement différent des systèmes d’isolation actuels, le premier chapitre dresse un état de l’art des métamatériaux, afin d’en comprendre les mécanismes et les méthodes numériques permettant d’en calculer les performances. Le deuxième chapitre aborde les techniques de caractérisation des matériaux employées pendant cette thèse. Les essais mécaniques ainsi que les résultats permettent de définir les modèles matériaux utilisés par la suite. Dans le troisième chapitre, des calculs numériques appliqués à différentes architectures aident à mieux comprendre certains mécanismes des métamatériaux et à choisir le meilleur candidat vis-à-vis des propriétés ciblées. Celui-ci est approfondi dans le quatrième chapitre, à travers des études paramétriques statiques et dynamiques. Des propositions d’améliorations géométriques sont proposées, y compris un métamatériau hybride aux propriétés supérieures. Afin de vérifier les résultats expérimentaux et d’acquérir une meilleure compréhension des mécanismes sous-jacents, le cinquième chapitre aborde finalement les essais expérimentaux effectués, l’analyse de leurs résultats, et leur confrontation avec les résultats numériques
Metamaterials are architectured materials exhibiting exotic properties due to their internal stucture rather than their constitutive material. They have now been studied for two decades, but have yet to make their mark outside laboratories, especially for industrial applications. This thesis focuses on elastic metamaterials that can contribute to fix vibration issues in the automotive field. Better isolation of the main vibration sources would increase both the vibroacoustic comfort in the vehicles and the safety of mechanical parts. Through computations and experimentations, it is shown that metamaterials can be designed to meet different criteria usually contradictory and as such, are strong candidates for innovative breakthroughs in industry. As this kind of solutions differs radically from existing ones, the first chapter is a state-of-the-art review, both to grasp the main mechanims behind the multitude of metamaterials designs that can be found in the literature, as well as the methods used to modelize them. The second chapter tackles the characterization of the materials used along this thesis. The mechanical tests and results presented allow to determine the material models then inserted in the computations. Through preliminary computations, the third chapter attempts to understand and select the most promising mechanisms to satisfy the expected specifications. The chosen design properties are further investigated in the fourth chapter, through static and dynamic computations, as well as parametric studies. A hybrid metamaterial with enhanced isolation properties is proposed. To finally assess the numerical results obtained and reach better undestanding of the underlying mechanisms, the fifth chapter deals with the performed experimental tests, their analysis, and their comparison with previous results

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Terroir, Arthur. "Étude et réalisation de métamatériaux acoustiques architecturés." Thesis, Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILN008.

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Dans le cadre de l'acoustique sous-marine, la détection de bâtiments est aujourd'hui un sujet largement étudié. Les revêtements de coques permettent d'échapper à cette détection mais il est nécessaire d'améliorer leurs performances pour suivre le développement des systèmes SONAR, en particulier pour les basses fréquences.Les métamatériaux sont utilisés dans ce but pour leurs propriétés de filtrage fréquentiel et de résonance locale. Cependant une autre stratégie consiste à s'intéresser aux métamatériaux architecturés permettant l'obtention de propriétés mécaniques hors du commun, par exemple un coefficient de Poisson anti-auxétique, c’est-à-dire supérieur à 0,5.Dans cette thèse, une structure permettant d'obtenir de tels coefficients de Poisson est étudiée, dans le cas de volumes infinis puis adaptée au cas de plaques d'épaisseur finie, par des outils numériques basés sur la simulation éléments finis. Une méthode d'homogénéisation dans la limite des grandes longueurs d’onde est développée à partir des outils numériques en exploitant les courbes de dispersion et est utilisée pour obtenir les propriétés effectives de la structure aussi bien en volume qu'en plaque. Dans le cas de la plaque, le modèle est adapté afin de prendre en compte une densité matricielle. La structure en plaque est ensuite caractérisée en statique par des essais en traction et en dynamique par l'identification des modes de flexion. Ces tests permettent de mettre en évidence les limites de validité du modèle d’homogénéisation. Enfin, des revêtements sont conçus à partir de la structure architecturée pour répondre aux objectifs de performances fixés, notamment en basses fréquences, pour la furtivité sous-marine. Plusieurs panneaux sont alors proposés
In the framework of underwater acoustics, detection of submerged vehicles is widely studied. Hull coatings are used to avoid such detection. Due to the enhancement of SONAR system low frequency performance, hull coatings must be improved.Acoustic metamaterials can be useful for this purpose thanks to their stop-band effect and local resonances. Alternatively, other types of metamaterials can be explored. A novel approach consists in exploring architectured metamaterials allowing outstanding mechanical properties, such as anti-auxetic Poisson's ratios greater than 0.5.In this thesis, a structure exhibiting anti-auxetic Poisson's ratios is studied using the finite element method. The study is conducted on the one hand for infinite volumes and on the other hand for finite thickness plates. An homogenization method is developed to obtain the effective properties of the structure in the low frequency domain using numerical tools based on the structure’s dispersion curves. The effective properties are determined for both infinite volumes and finite plates. Those determined in the case of plates are adapted in order to take into account an anisotropic density. The plates are then characterized experimentally using two methods. First a static characterization is performed through a tensile test. Then a dynamic characterization through an identification of the flexural modes is conducted. Those measurements allow to define limits of validity for the homogenization model. Finally, hull coatings based on the architectured structure are designed in order to reach the performance objectives for underwater stealth, mainly in low frequency. Several panels are then proposed

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(9006635), Debkalpa Goswami. "Design and Manufacturing of Flexible Optical and Mechanical Metamaterials." Thesis, 2020.

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Анотація:

Metamaterials are artificially structured materials which attain their unconventional macroscopic properties from their cellular configuration rather than their constituent chemical composition. The judicious design of this cellular structure opens the possibility to program and control the optical, mechanical, acoustic, or thermal responses of metamaterials. This Ph.D. dissertation focuses on scalable design and manufacturing strategies for optical and mechanical metamaterials.

The fabrication of optical metamaterials still relies heavily on low-throughput process such as electron beam lithography, which is a serial technique. Thus, there is a growing need for the development of high-throughput, parallel processes to make the fabrication of optical metamaterials more accessible and cost-effective. The first part of this dissertation presents a scalable manufacturing method, termed “roll-to-roll laser induced superplasticity” (R2RLIS), for the production of flexible optical metamaterials, specifically metallic near-perfect absorbers. R2RLIS enables the rapid and inexpensive fabrication of ultra-smooth metallic nanostructures over large areas using conventional CO₂ engravers or inexpensive diode lasers. Using low-cost metal/epoxy nanomolds, the minimum feature size obtained by R2RLIS was <40 nm, facilitating the rapid fabrication of flexible near-perfect absorbers at visible frequencies with the capability to wrap around non-planar surfaces.

The existing approaches for designing mechanical metamaterials are mostly ad hoc, and rely heavily on intuition and trial-and-error. A rational and systematic approach to create functional and programmable mechanical metamaterials is therefore desirable to unlock the vast design space of mechanical properties. The second part of this dissertation introduces a systematic, algorithmic design strategy based on Voronoi tessellation to create architected soft machines (ASMs) and twisting mechanical metamaterials (TMMs) with programmable motion and properties. ASMs are a new class of soft machines that benefit from their 3D-architected structure to expand the range of mechanical properties and behaviors achievable by 3D printed soft robots. On tendon-based actuation, ASMs deform according to the topologically encoded buckling of their structure to produce a wide range of motions such as contraction, twisting, bending, and cyclic motion. TMMs are a new class of chiral mechanical metamaterials which exhibit compression-twist coupling, a property absent in isotropic materials. This property manifests macroscopically and is independent of the flexible material chosen to fabricate the TMM. The nature of this compression-twist coupling can be programmed by simply tuning two design parameters, giving access to distinct twisting regimes and tunable onset of auxetic (negative Poisson’s ratio) behavior. Taking a metamaterial approach toward the design of soft machines substantially increases their number of degrees of freedom in deformation, thus blurring the boundary between materials and machines.

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Тези доповідей конференцій з теми "Non-auxetic"

Mesa, Olga, Milena Stavric, Saurabh Mhatre, Jonathan Grinham, Sarah Norman, Allen Sayegh, and Martin Bechthold. "Non-Linear Matters: Auxetic Surfaces." In ACADIA 2017: Disciplines and Disruption. ACADIA, 2017. http://dx.doi.org/10.52842/conf.acadia.2017.392.

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Grzybek, Dariusz, Wojciech Sikora, Dariusz Kata, and Piotr Micek. "Comparative Numerical Analysis of a Piezoelectric Harvester Based on Non-auxetic and Auxetic Material." In 2020 21th International Carpathian Control Conference (ICCC). IEEE, 2020. http://dx.doi.org/10.1109/iccc49264.2020.9257264.

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Warisaya, Kanata, Hiroaki Hamanaka, Asao Tokolo, and Tomohiro Tachi. "Auxetic Structures Based on Rhombic Tiling." In ASME 2021 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/detc2021-67141.

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Abstract Auxetic material using corner-connected kinematic tiles has been applied to different kinematic designs. However, existing works rely on the connectivity of regular polygonal tilings because of the overconstraining nature of kinematic tiling. This study proposes a new family of auxetic structures based on non-regular and aperiodic rhombic tiling inspired by the Tokyo 2020 Emblems. We convert emblem-like patterns on rhombic tilings into kinematic structures by regarding the rectangular figure as voids and the region between rectangles as rigid bodies. Due to the geometric properties of rhombic tiling, the structure forms a one-degree-of-freedom planar mechanism with a constant Poisson’s ratio of −1. The large combinatorial family of rhombic tilings provides design variations of kinematic structures with non-regular topology. Furthermore, we show a kirigami-based method for fabricating the structure as a compliant mechanism. This connection between math and art potentially broadens the range of architected materials based on folding, kirigami, and tessellation.

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Lee, Chihun, Jaehyung Ju, and Doo-Man Kim. "The Dynamic Properties of a Non-Pneumatic Tire With Flexible Auxetic Honeycomb Spokes." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-88199.

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Motivated by our previous study on the flexibility and low local stress of auxetic hexagonal honeycombs in uni-axial loading, we explore the dynamic characteristics of a flexible auxetic hexagonal lattice structure when it is used as the flexible spokes of a non-pneumatic tire. In this study, a modal analysis and the steady state vibration characteristics of NPTs with cellular spokes are investigated with a series of vertical loads and rolling speeds using a commercial finite element code, ABAQUS/Explicit. The angular velocity and the displacement at the hub center and the reaction force on the ground were investigated in the time and frequency domains for the steady state rolling condition for vehicle speeds of 60km/h and 80km/h. The orthotropic properties of the honeycomb spokes create different modal behaviors compared with those of pneumatic tires; e.g., the in-plane shear at the initial mode. The discrete spoke geometry induces a non-homogeneous mass (non-uniformity) distribution, which also causes local vibration effects.

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Radics, Janos P., and Levente Szeles. "Investigating The Load-Bearing Capacity Of Additively Manufactured Lattice Structures." In 35th ECMS International Conference on Modelling and Simulation. ECMS, 2021. http://dx.doi.org/10.7148/2021-0133.

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Additive manufacturing provides unprecedented design freedom from the product’s external appearance to the internal structure. Additively manufactured parts, objects can be designed with cellular lattice structures as infills. The application of lattice structures can reduce the required amount of material and desired properties can be assigned to certain objects. There are several different lattice structures each with its own unique, exclusive property or properties. In this study a wide spectrum of so called ‘auxetic’ and standard lattice structures will be compared using finite element method and compression laboratory tests. The considered auxetic and non-auxetic cellular structures are based on the result of other researches. Along with the aforementioned existing lattices several new structures were proposed. Nine distinct additively manufactured specimens were compared.

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Yang, Chulho, Hitesh D. Vora, and Young Bae Chang. "Evaluation of Auxetic Polymeric Structures for Use in Protective Pads." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-67588.

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Auxetic materials, known as materials with negative Poisson’s ratio (NPR), have many promising application areas. However, there are only few natural and man-made materials such as certain living bone tissues, certain rocks and minerals, polymeric honeycombs, microporous polytetrafluoroethylene (PTFE), foams, and carbon-fiber-reinforced epoxy composite laminate panels that possess this property. In recent years, various auxetic material structures have been designed and fabricated for diverse applications that utilized normal materials which follow Hooke’s law but still show the NPR properties. One of the applications is body protection pads that are comfortable to wear and effective in protecting body parts by reducing impact force and preventing injuries in high-risk individuals such as elderly people, industry workers, law enforcement and military personnel, and sports players. It is important to develop new body protectors that best combine each individual’s requirements for wearing comfort (flexible, light-weight), ease of fitting (customized), ensured protection, and cost-effectiveness. The protection pad would be made from multilayer materials and adaptive structures to achieve unique multifunctional properties such as high hardness, impact toughness, light weight, and excellent shock absorption suitable for the needs. This paper reports an integrated theoretical, computational (finite element analysis), and experimental investigation conducted for typical auxetic polymeric materials that exhibit negative Poisson’s ratio (NPR) effect. Parametric 3D CAD models of auxetic polymeric structures such as re-entrant hexagonal cells and arrowhead were developed. Then, key structural characteristics of protectors were evaluated through static analyses of FEA models. In addition, impact/shock analyses were conducted through dynamic analyses of FEA models to validate the results obtained from the static analyses. Particularly, an advanced additive manufacturing (3D printing) technique was used to build prototypes of the auxetic polymeric structures. Specifically, three different materials typically used for FDM (Fused Deposition Modeling) technology such as Polylactic acid (PLA) and thermoplastic polyurethane (TPU) material (NinjaFlex® and SemiFlex®) were used for different stiffness and shock-absorption performances. The 3D printed prototypes were then tested and the results were compared with the computational prediction. The results showed that the auxetic material can be effective for body protection pads. Each structure and material had unique structural properties such as stiffness, Poisson’s ratio, and efficiency in shock absorption. Particularly, auxtetic structures showed better shock absorption performance than non-auxetic ones. The mechanism for ideal input force distribution or shunting could be suggested for designing protectors using various shapes, thicknesses, and materials of auxetic materials to reduce the risk of injury.

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Ardebili, Mahmoud K., Kerim Tuna Ikikardaslar, Erik Chauca, and Feridun Delale. "Behavior of Soft 3D-Printed Auxetic Structures Under Various Loading Conditions." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87859.

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Auxetic structures exhibiting non-linear deformation are a prevalent research topic in the material sciences due to their negative Poisson’s ratio. The auxetic behavior is most efficiently accomplished through buckling or hinging of 3d printed structures created with soft or flexible materials. These structures have been hypothesized to have some unique characteristics and may provide advantages over conventional engineering materials in certain applications. The objective of present study is to gain a better understanding of behavior of auxetic structures subjected to tensile, compressive and impact loads and assess geometric parameters affecting these structures in applications such as impact shielding or biomedicine. Analytical and experimental methods were employed to investigate two different types of auxetic structures which were 3d-printed with TPU (thermoplastic polyurethane). The first was based on symmetric re-entrant angles cells patterned to form sheet-like structure. Rotation of members in opposite directions in a cell induces negative Poisson’s ratio when the structure is subjected to tensile loading. The second structure was based on rectangular lattice of circular holes. This structure exhibited auxeticity due to formation of pattern of alternating mutually orthogonal ellipses when subjected to compressive and impact loads. Parameters of interest in this study included hardness of the plastic used in printing the structures, the fill pattern of 3d-printed solid parts, porosity of cylinders in the lattice structure, angles and thickness of members in the re-entrant structure. Preliminary results indicated that per unit weight of material, the re-entrant structure requires less tensile load to strain than a solid structure. This is advantageous in applications where expansion in lateral direction is required. The lattice of circular holes structure exhibited similar trend in impact and compressive loading. The results indicate that geometric parameters influence auxeticity of the structure a great deal. When the porosity of the lattice is too small, positive Poisson’s ratio is observed. The length to height ratio of the re-entrant cell has similar effect on the structure’s Poisson’s ratio. The main advantage gained by employing such structures is their overall ability to resist buckling and withstand impact load without cracking. This study will help to develop 3D-printing techniques in manufacturing better performing structures under similar conditions.

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Flores, Wilmer, Andres Curbelo, Luisana Calderon, Jayanta S. Kapat, and Kareem Ahmed. "Adiabatic Film Cooling Effectiveness Measurement of High Performance Combustion Liner Slot Jets." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91783.

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Abstract The present study experimentally investigates adiabatic film cooling effectiveness for high performance flow auxetic geometries (S-Slot and Ellipsoid). Both geometries are auxetic structures that were designed around a Negative Poisson Ratio (NPR). Manufactured NPR combustion liners offer higher quality fracture resistance [1] and high energy absorption [2]. Film cooling effectiveness results for test geometries were non-dimensionalized by a baseline case of circular inline orifices. Non-intrusive pressure sensitive paint (PSP) technique was utilized to obtain local surface pressure gradients for each experimental geometry. Adiabatic film cooling effectiveness measurements were tested for multiple blowing ratios (BR) ranging between 0.05–1.15. Three plate configurations were studied with void inclination angles of 0 degrees. Analyses demonstrate that blowing ratios of 0.5 and 0.75 are optimal for S-slot adiabatic effectiveness. Film cooling results for the Ellipse configuration show increasing effectiveness up to an optimal blowing ratio of 0.5, and decreases as BR is increased beyond that. Additional experiments were performed by keeping the differential pressure across the plates constant. Results indicate that the S-slot provides optimum film cooling effectiveness while the differential pressure conserved in comparison to Ellipses and Circles.

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Li, Pu, Jingxia Yue, Xiaobin Li, and Wenchao Wan. "Axial Compression and Collapse Properties of 3D Re-Entrant Hexagonal Auxetic Structures." In ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/omae2020-18418.

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Abstract A three-dimension (3D) re-entrant honeycomb structure which exhibits negative Poisson’s ratio in all three principal directions is modeled from a classical two-dimension (2D) auxetic material. In this work, on the basis of the Castigliano’s second theorem and Timoshenko beam model, the shear deformation and axial deformation of this structure are investigated. And the analytical formulas of the effective modulus and Poisson’s ratio in each principal direction of the honeycomb structure are derived. By comparing the analytical results with the finite element analysis results, the rationality of the formula is verified. Then, the collapse characteristics of honeycomb structures with different mechanical properties under variation impact velocities are studied. The results show that, the deformation of honeycomb structure can be divided into three patterns, “quasi-static” deformation, “transitional” deformation and “local” deformation varied with impact velocities. And due to inertial effect, with the increase of impact velocity, the load-bearing capacity and energy absorption of the structure also increased. In addition to the impact velocity, the cells’ configuration is also a non-negligible factor, and its turns out that the decrease of angle accelerates the deformation state of the honeycomb structure and strengthen the energy-absorption capability after being subjected to impact load.

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Mehta, Vipul, Mary Frecker, and George Lesieutre. "Stress Relief in Contact-Aided Cellular Compliant Mechanisms." In ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2008. http://dx.doi.org/10.1115/smasis2008-431.

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Cellular structures with an internal contact-mechanism are investigated. These contact-aided compliant mechanisms are shown to reduce the local tensile stresses, thereby providing additional global strain before yielding or fracture failure compared to honeycomb or auxetic cellular structures. An analytical model for such structures is developed and it is validated using FEA simulations. Two different materials are considered for comparison. More than 100% improvement in global strain capability is possible using the contact. A high-strain morphing aircraft skin is examined as an application of these mechanisms. The contact-aided cellular compliant mechanisms are more advantageous in terms of both the structural mass as well as the global strain compared to a non-contact design. In the application considered the stress-relief mechanism increased the global strain capability by as high as 37%.

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