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1

Chen, Da. "A Multi-Material Projection Stereolithography System for Manufacturing Programmable Negative Poissons Ratio Structures." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/74961.

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Digital light Projection based Additive Manufacturing (AM) enables fabrication of complex three-dimensional (3D) geometries for applications ranging from rapid prototyping jet parts to scaffolds for cell cultures. Despite the ability in producing complex, three-dimensional architectures, the state of art DLP AM systems is limited to a single homogenous photo-polymer and it requires a large volume of resin bath to begin with. Extensible Multi-material Stereolithography (EMSL) is a novel high-resolution projection stereolithography system capable of manufacturing hybrid 3D objects. This system provides new capabilities, allowing more flexible design criteria through the incorporation of multiple feedstock materials throughout the structure. With EMSL manufacturing ability, multi-material programmable negative Poissons ratio honeycomb reentrant structures are realized. Researchers have been studying auxetic structures over decades, the mechanical property control of auxetic structure mainly relies on geometry design in previous studies. Now with the help of EMSL system, other design variables associated with auxetic structures, such as material properties of local structural members, are added into design process. The additional variables are then proved to have significant effects on the material properties of the auxetic structures. The ability to accurately manufacture multi-material digital design will not only allow for novel mechanical and material researches in laboratory, but also extend the additive manufacturing technology to numerous future applications with characteristics such as multiple electrical, electromechanical and biological properties. The design and optimization of EMSL system realizes novel structures have not been producible, therefore it will stimulate new possibilities for future additive manufacturing development.<br>Master of Science
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2

Heo, Hyeonu. "Programmable Mechanical Metamaterials with Negative Poisson's Ratio and Negative Thermal Expansion." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955088/.

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Programmable matter is a material whose properties can be programmed to achieve particular shapes or mechanical properties upon command. This is an essential technique that could one day lead to morphing aircraft and ground vehicles. Metamaterials are the rationally designed artificial materials whose properties are not observed in nature. Their properties are typically controlled by geometry rather than chemical compositions. Combining metamaterials with a programmable function will create a new area in the intelligent material design. The objective of this study is to design and demonstrate a tunable metamaterial and to investigate its thermo-mechanical behavior. An integrated approach to the metamaterial design was used with analytical modeling, numerical simulation, and experimental demonstration. The dynamic thermo-mechanical analysis was used to measure base materials' modulus and thermal expansion coefficient as a function of temperature. CPS, the unit cell of the metamaterial, is composed of circular holes and slits. By decomposing kinematic rotation of the arm and elastic deformation of a bi-material hinge, thermo-mechanical constitutive models of CPS were developed and it was extended to 3D polyhedral structures for securing isotropic properties. Finite element based numerical simulations of CPS and polyhedral models were conducted for comparison with the analytical model. 3D printing of multi-materials was used for sample fabrication followed by tests with uniaxial compressive mechanical tests and thermal tests at 50℃. From the analytical model of the metamaterial, the contour plots were obtained for the effective properties – Poisson's ratio, the effective coefficient of thermal expansion of the metamaterial as a function of geometry and materials. A controllable range of temperature and strain was identified associated with maximized thermal expansion mismatch and contact on the slit surface of CPS, respectively. This work will pave the road toward the design of programmable metamaterials with both mechanically- and thermally- tunable capability and provide unique thermo-mechanical properties with a programmable function.
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3

Jayanty, Sharmila. "Negative Poisson’s Ratio Composites - Finite Element Modeling and Experiments." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1290137957.

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4

Asad, Mohammad. "Failure analysis and mitigating strategies for masonry walls subject to vehicular impacts." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/201381/1/Mohammad_Asad_Thesis.pdf.

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This thesis demonstrates how new materials and damping technologies were developed and applied to mitigate the adverse effects of vehicular crashes into masonry buildings. Many masonry buildings are vulnerable to vehicular crashes which result in loss of property, loss of habitat or functionality of the building and harm to the occupants of the building and vehicle. Auxetic materials were used in this research with negative Poisson ratio and innovative damping technologies at the wall edges to reduce the accident severity and to save the lives in both the building and the vehicle.
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5

Donoghue, John Philip. "Negative Poisson's ration effects on the mechanical performance of composite laminates." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367283.

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6

Siddorn, Mark J. "Classifying and identifying negative Poisson's ratio : an examination of the auxeticity in zeolitic materials." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/17323.

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The aim of this thesis is to advance the understanding of auxeticity. This is achieved by developing a more accurate way to classify materials exhibiting the property, by carrying out high-throughput atomistic simulations of framework materials based on the SiO2 and GeO2 chemistries, and by exploring mechanistic models and possible correlations with directional density variations. At first this thesis outlines the development of a typographic system for negative Poisson's ratio. Materials are given classifications based on the degree to which auxetic behaviour is observed along specific axes of deformation and the frequency of occurrence of these axes. A systematic study is then performed on the elastic properties of zeolitic silicon dioxide and germanium dioxide structures. The typology is applied to these materials to better understand their auxetic behaviour. The JST framework is identified as isotropically auxetic, the first crystal to exhibit such general negative Poisson's ratios. An exploration into the effects of local density variations between parallel planes on Poisson's ratio is undertaken, but no clear correlation is found. Finally, software for systematically creating and evaluating two dimensional networks of triangles is produced. The geometrical analysis of these rotating structures predicts a high level of auxeticity and further work into three dimensional equivalents is recommended.
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7

Matheny, Julie C. "Understanding the Transition from Positive to Negative Poisson's Ratio Behavior in Cellular Materials and the Potential for Auxeticity in Trabecular Bone." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1310140272.

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8

Baker, Carrie E. "Auxetic Spinal Implants: Consideration of Negative Poisson's Ratio in the Design of an Artificial Intervertebral Disc." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1302099679.

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9

Kamarsu, Prasanth R. "Towards Developing a Technique to Produce Nanocomposites with Uniform Auxetic Behavior." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1310136514.

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10

Postma, Tiemen Rudolf. "Innovative laminate structures for tubular elements." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579514.

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The performance of peristaltic pumps is mainly governed by their tubing or hose materials. Research and development in this area is therefore very important for peristaltic pump manufacturers to keep in front of the competition and to open up new applications to enable further market penetration. Another aspect of this is of course price; performance and cost have to be in balance. As an approach to fabricate a new tube material, the field of negative Poisson's ratio (or: auxetic) materials is explored. The combined deformations of tensile, compression and shear in a peristaltic pump tube may well benefit from the specific characteristics of auxetic materials. Materials can be designed to keep their dimensions constant in directions perpendicular to an applied load. This is referred to as “auxetic balancing”. Finite element modelling shows that lowering the Poisson's ratio will rapidly decrease the maximum stresses in the cross-section of an occluded tube. Optimum values for the Poisson's ratio are found to be between −0.1 and +0.1, preferentially being 0. The re-entrant honeycomb structure is selected for initial trials, but manufacturing of this structure at the desired dimension proved to be too difficult at this time. Instead, electrospun nanofibre membranes are selected as the reinforcement structure. A liquid silicone elastomer is used as the matrix material. Key characteristics for the new material are derived from baseline test results on existing tubing. Laminates are manufactured from electrospun nylon6 nanofibre membranes coated with a liquid silicone rubber. Compression moulding is used to cure the nylon6-silicone rubber laminate, to give two effects: it ensures impregnation of the membrane and the compression deforms the nanofibre structure in such a way that it will become auxetic through-the-thickness. Flat sheet laminates of 2 mm thickness are manufactured with 14 layers of reinforcement. A reinforcing effect and substantial lowering of the through-the-thickness Poisson's ratio is observed for the laminates at low strains. At higher strains (>50%) the effect of the reinforcement diminishes and the Poisson's ratio of the laminate and pure silicone rubber equalises. Finally, tubular laminates are manufactured and the resulting tubes are tested in a peristaltic pump with some promising results (>1 million occlusions before failure). Tube performance is not yet at the required level, but with further optimisation of the laminating process, mould design and (post-)curing large steps forward can be made.
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11

Rettiganti, Mallikarjuna Rao. "Statistical Models for Count Data from Multiple Sclerosis Clinical Trials and their Applications." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1291180207.

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12

Zahra, Tatheer. "Strategies for improving the response of drystack masonry to compression." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/109907/1/Tatheer_Zahra_Thesis.pdf.

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Drystack or mortarless walling can be constructed faster with less skilled labour compared to the traditional mortared masonry walls; however, the contact surface unevenness of the blocks affects the constructability of drystack system. This thesis is aimed at studying the contact surface properties of drystack masonry and to propose suitable mitigation through systematic experimental and numerical studies so that this masonry type could be constructed with ease and used as a structural system. New genre composite materials are proposed to improve the performance of drystack masonry by embedding between the blocks and by providing protective layering on the drystack walls.
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13

Brandel, Brian Peter. "Processing and testing of negative Poisson's ratio polyethylene foams /." 1999. http://catalog.hathitrust.org/api/volumes/oclc/44538817.html.

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Thesis (M.S.)--University of Wisconsin--Madison, 1999.<br>Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 95-101).
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14

Xu, Jun-Wei, and 許俊偉. "Innovative Infill Structures with Negative Poisson’s Ratio for Fused Deposition Modeling Parts." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/kpd65v.

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碩士<br>國立聯合大學<br>機械工程學系碩士班<br>107<br>FDM (fused deposition modelling) is a 3D printing method which uses continuous filaments of thermoplastic material to construct solid parts. Structures with NPR (negative Poisson’s ratio) can be easily printed out using FDM technique. However, the feature of NPR is usually two dimensional and in-plane. This study changed the internal fill structure of 3D printing to create a woven NPR internal fill, which is shaped close to the cross mesh and can have NPR in the Z-axis direction. Due to the improved elasticity of NPR structure, according to the rubber and elastomer test specifications, the effects of different arrangement and fiber length on the NPR test film were detected, and the impact moment was analyzed using simulation results. Through simulation can be found Poisson’s ratio and internal reactions, and the Taguchi method to find out the largest rebound structure of the printing parameters, the long fiber's rebound resilience is about five times higher, and the short fiber is about doubled.
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15

Ling, Yiru. "Investigation on Effects of Geometric Parameters on the Negative Poisson’s Ratio of a Reentrant Structure." Master's thesis, 2017. http://hdl.handle.net/1885/117205.

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It is not common to find negative Poisson’s ratio in nature but it exists in auxetic materials. The auxetic property enables the material to elongate in both vertical and horizontal directions under tension. Cellular honeycombs with repetitive reentrant cells are a common example of auxetics. This thesis investigates the geometric impacts of a reentrant structure originating from honeycombs on the negative Poisson’s ratio of the structure. Finite Element Method is used for the simulation, with the commercial software ANSYS APDL 15.0. The negative Poisson’s ratios under different geometric parameters are discussed based on the simulation results with small displacement and linear plane elements. Geometric non-linearity is also taken into consideration for large displacement which occurs in the experiments. Non-linear plane elements are used in the simulation with non-linear geometric deformations. Experimental Poisson’s ratios are collected from tension tests conducted on 3D printed reentrant honeycomb structures, to evaluate the simulation’s accuracy. The simulated results do reflect the same trend in the geometric effects on the negative Poisson’s ratio compared to the corresponding experimental cases, although, there are numerical discrepancies between simulation and experiments. Causes of the differences are analysed. Possible improvements which can be carried out in the future are suggested.
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16

Chen, Yaw-Tyng, and 陳耀庭. "The design and analysis method of the mechanism by using the theorem of negative Poisson's ratio." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/50535081419239759469.

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17

Steffens, F. "Desenvolvimento de estruturas fibrosas com comportamento auxético." Doctoral thesis, 2015. http://hdl.handle.net/1822/38488.

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Tese de Doutoramento Engenharia Têxtil<br>Os materiais auxéticos diferenciam-se dos convencionais por apresentarem como característica principal, o coeficiente de Poisson negativo. Consequentemente, possuem um comportamento incomum: quando tensionados longitudinalmente aumentam a sua seção transversal. Este comportamento faz com que sejam interessantes em diversas áreas de aplicação onde a absorção de energia de impacto e as resistências ao corte, perfuração e abrasão sejam fatores determinantes, incluindo: vestuário de proteção em diversos domínios, material militar, materiais balísticos, isolamentos acústicos, sistemas de proteção contra explosivos, entre outros. O objetivo principal deste trabalho é o desenvolvimento de estruturas fibrosas de alto desempenho com comportamento auxético, a partir da tecnologia de produção de malhas de trama. Para isso, foi estudada a influência da composição do material, do comprimento de laçada e da tensão de tiragem sobre o coeficiente de Poisson negativo de malhas produzidas a partir de para-aramida, poliamida de alta tenacidade e híbridas. Foram também estabelecidas as correlações entre o efeito auxético das malhas produzidas e os parâmetros estudados: fator de cobertura, densidade de fileiras e colunas, espessura e resistência à tração. Outro aspeto importante abordado nesta tese foi a possibilidade de aplicação das estruturas têxteis auxéticas como camada de absorção de energia em vestuário de proteção ao corte, especificadamente para utilizadores de motosserra. Foi ainda estudado a combinação entre estruturas fibrosas auxéticas baseadas em malha de trama e matrizes poliméricas de poliéster e epóxida. Neste sentido, pretendeu-se investigar a transferência da característica auxética das malhas para os materiais compósitos por elas reforçados. Os resultados obtidos evidenciaram que a tensão de tiragem, o comprimento da laçada, bem como o tipo de matéria-prima utilizada possuem influência marcante nos valores do coeficiente de Poisson negativo das malhas desenvolvidas. Verificou-se, ainda, que a aplicação das malhas auxéticas demonstrou grande potencialidade na proteção ao corte quando comparadas com estruturas convencionais. Além disso, foi possível a transferência do efeito auxético obtido nas malhas aos compósitos desenvolvidos, tanto com a resina epóxida quanto com a de poliéster. Desta forma, este trabalho procurou contribuir para o avanço do conhecimento sobre produção, ensaio e comportamento de estruturas fibrosas auxéticas baseadas em malhas de trama, demonstrando que a exploração científica destes novos materiais pode proporcionar a obtenção de produtos têxteis diferenciados para os diversos campos industriais, especificamente para a área de proteção.<br>Auxetic materials differ from conventional ones for presenting the negative Poisson’s ratio as their main property. Consequently, these materials have an unusual behavior: when longitudinally stretched, there’s an increase on their transversal section. This behavior makes them interesting in many areas of application where the impact energy absorption and cut, perforation and abrasion resistance are key factors, including: protective clothing in many areas, military gear, ballistic protection, soundproofing, explosion protection systems, among others. The main objective of this study was to develop fibrous structures based on high performance yarns with auxetic behavior using weft knitting technology. In order to achieve this objective, the influence of the material’s composition, loop length and take-down value were studied on the negative Poisson’s ratio presented by knitting produced from para-aramid, high tenacity polyamide and hybrid ones. The correlations between the auxetic effect and parameters like cover factor, knitting density, thickness and tensile strength were also thoroughly analyzed. Another relevant aspect discussed on this work was the possibility of applying auxetic textile structures as an energy absorption layer on cut-resistant protective clothing, specifically forchainsaw operators. The combination between fibrous auxetic structures based on weft knitted and polyester and epoxy polymeric matrices was also studied. On this matter, the transference of the auxetic behavior from knitting fabric to the composite materials reinforcedby them was also investigated. The results obtained showed that the take-down, the loop length, as well as the type of raw material employed present remarkable impact on the negative Poisson’s ration of the knitted fabrics developed. It was also verified that the application of auxetic knitted fabric present great potential on cut protection when compared to conventional structures. Furthermore, the transference of the auxetic effect obtained on the knitting fabric to the developed composites was possible with both epoxy and polyester resins. Thus, this study proposed to contribute to the progress on knowledge about production, testing and behavior of fibrous auxetic structures based on weft knitting technology, intending to show that the scientific exploration of these new materials may lead to the development add value textile products for several industrial fields, including protection.<br>Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES)
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18

Silva, Daniela Barras Nunes Serra e. "Additive Fabrication of 3D Anepectic Structures." Master's thesis, 2021. http://hdl.handle.net/10362/129350.

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This work focuses on the design and manufacture (by additive fabrication) of 3D anepectic structures. These anepectic structures have two rare characteristics: they exhibit negative values of Poisson’s ratio and of coefficient of thermal expansion (CTE). Negative values of CTE are activated by the combination of two different materials, in which both have positive values of CTE. This type of structure is useful in applications such as in the biomedical and aerospace fields, where it is important to have a mechanical response to a thermal stimulus. Ten samples were studied and subjected to thermo-mechanical tests: five single material samples (four of Nylon and one of CPE+) and five dual material samples (four of Nylon-PVA and one of Nylon-CPE+). All samples were subjected to tensile tests in which the most negative value of Poisson’s Ratio achieved in this work was of -1.103. All samples were subjected to thermal tests, in which they were submerged in silicone oil (Baysilone M350) and, then, subjected to a heating process. In this type of test, the most negative value of CTE was of -812× 106 /º𝐶 at 120ºC. Palavras-chave: Impressão 3D, Auxética, Expansão térmica negativa, Anepéctica, Coeficiente de Poisson negativo.<br>Este trabalho foca-se no desenho e fabricação (por fabricação aditiva) de estruturas anepécticas 3D. Essas estruturas anepécticas possuem duas características raras: apresentam valores negativos de coeficiente de Poisson e de coeficiente de expansão térmica (CET). Valores negativos de CET são ativados pela combinação de dois materiais diferentes, no qual ambos têm valores positivos de CET. Este tipo de estrutura é útil em aplicações como na área biomédica e aerospacial, onde é importante ter uma resposta mecânica a um estímulo térmico. Dez amostras foram estudadas e submetidas a testes termo-mecânicos: cinco amostras de um só material (quatro de Nylon e uma de CPE+) e cinco amostras de dois materiais (quatro de NylonPVA e uma de Nylon-CPE+). Todas as amostras foram submetidas a ensaios de tração em que o valor mais negativo do coeficiente de Poisson obtido neste trabalho foi de -1.103. Todas as amostras foram submetidas a testes térmicos, em que foram imersas em óleo de silicone (Baysilone M350) e sujeitas a um processo de aquecimento. Neste tipo de teste, o valor mais negativo de CTE foi de −812 × 10−6 /ºC a 120ºC.
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19

Raminhos, Joana Maria Santos. "Additive Fabrication of Anepectic Meshes." Master's thesis, 2018. http://hdl.handle.net/10362/56321.

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This work applies additive manufacturing technology to fabricate bi-dimensional lightweight composite anepectic meshes capable of demonstrating auxetic properties (negative Poisson’s ratio (NPR)) in combination with negative thermal expansion (NTE) behaviour, using as constituent materials polymers that do not exhibit NTE behaviour. Each mesh, obtained from varying either the material combination or the design parameter, was tested on a heated silicone bath to study the effects of the different combinations on the coefficient of thermal expansion (CTE). Photographs were taken at different stages during the heating process and were analysed to determine the CTE of each mesh. It was found that all composite meshes studied demonstrated a successful combination of NPR and NTE behaviours, and it was revealed that there is a possibility to tailor the meshes to activate the NTE behaviour within a chosen range of temperatures. For an extreme case, a Poisson’s ratio of −0.06, along with a CTE of −1568  10-6 (ºC-1) has been achieved. These meshes may be applied to structures and equipment in which the disparity in thermal stress has be carefully managed to extend the life of the device, and also to produce biomedical devices such as stents, surgical hernia meshes (SHM), compression garments and others, with many advantages over current designs, namely the ability to counteract any relaxation effects resulting from increases in the service temperature.
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Catatão, Gonçalo Miguel Rodrigues. "Additive Manufacturing and Characterization of Three-dimensional Anepectic Structures." Master's thesis, 2022. http://hdl.handle.net/10362/134774.

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In recent years there has been an increase of interest in 3D anepectic structures. An anepectic structure is a metamaterial with auxetic behaviour (Negative Poisson's Ratio (NPR)) and negative coefficient of thermal expansion (CTE). This work intends to manufacture and characterize a 3D anepectic structure using materials with positive CTE. A known auxetic structure was used, in which a second material was incorporated to obtain a negative CTE. To achieve the design used in this work, mechanical and thermal finite element simulations were performed to preview the thermomechanical behaviour. The 3D anepectic structures were produced by additive manufacturing using polyvinyl alcohol and Nylon. Two models with different designs were developed. Its characterization necessitated the development of new methodologies to determine the Poisson's ratio (PR) and CTE. One of the models obtained the intended anepectic behaviour. Furthermore, there was a correlation between PR values and the number of cells in the structure. Until this day, this is the first published report of a manufactured and characterized 3D anepectic structure, making this work innovative in the area of metamaterials.<br>Nos últimos anos tem existido um aumento de interesse em estruturas anepécticas 3D, isto é, auxéticas (Coeficiente de Poisson negativo (NPR)) e com coeficiente de expansão térmica (CTE) negativo. Este trabalho pretende manufaturar e caracterizar uma estrutura anepéctica 3D, constituída por materiais com CTE positivos. Foi utilizado uma estrutura auxética conhecida, no qual se incorporou um segundo material com o intuito de obter um CTE negativo. Para obter esse design, realizou-se simulação mecânica e térmica de elementos finitos. As estruturas anepécticas 3D foram produzidas por fabricação aditiva utilizando PVA e Nylon. Foi desenvolvido dois modelos com diferentes designs. Para a sua caraterização foi necessário desenvolver metodologias novas para a determinação do PR e do CTE. Sendo que um dos modelos obteve o comportamento anepéctico pretendido. Para além disso, verificouse uma correlação entre os valores de PR e o número de células na estrutura. Até à data, esta é a primeira publicação de uma estrutura anepéctica 3D manufaturada e caraterizada. Tornando este trabalho inovador na área dos metamateriais.
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Páscoa, Frederico Tomás. "Development of Methodology for Modelling and Simulation of 3D Auxetic Structures." Master's thesis, 2021. http://hdl.handle.net/10362/135860.

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As the requirements associated with mechanical behavior in structures throughout all industries become more demanding, some of the improvement needs cannot be fulfilled without exploring geometries that behave in ways which are not commonly observed. One of the behaviors that can lead to breakthroughs in several fields is the auxetic behavior, which is present in auxetic structures. With most of the basic auxetic structures, the modelling and the simulation of the mechanical behavior can be performed with methods that do not require further improvements to work. But with complex auxetic structures, the application of these methods can be insufficient for constructing models which accurately define the structures. This makes these models inadequate for use in simulations of the behavior of said structures. This work proposes a methodology that allows for the modelling of complex three dimensional functionally graded auxetic structures, realized through modifications in the equations that define the basic surfaces which characterize the aforementioned structures. In this methodology, the simulation studies are performed by means of the finite element method. The gyroid surface was used as the complex geometry from which to form the auxetic structures. Experimental testing and simulation studies were performed on geometries with different gradient types and steepness’s to obtain comprehensive data that allows to infer on the accuracy of the methodology.<br>Com o aumento da exigência nos requisitos associados ao comportamento mecânico de estruturas em todas as indústrias, algumas das necessidades de progresso não podem ser colmatadas sem explorar geometrias que se comportam de maneiras que não são comummente observadas. Um dos comportamentos que poderá levar a avanços em vários ramos é o comportamento auxético, que está presente em estruturas auxéticas. No caso das estruturas auxéticas mais básicas, a modelação e a simulação do comportamento mecânico podem ser realizados com métodos que não requerem mais melhorias para funcionarem. Mas em estruturas auxéticas complexas, a aplicação destes métodos pode ser insuficiente para construir modelos que definam as estruturas de forma precisa. Isto torna estes modelos inadequados para utilizar em simulações do comportamento destas estruturas. Este trabalho propõe uma metodologia que permite modelar estruturas auxéticas complexas tridimensionais com gradiente funcional, realizada através de modificações nas equações que definem as superfícies base que caracterizam as estruturas mencionadas. Nesta metodologia, os estudos de simulação são realizados através do método dos elementos finitos. A superfície giróide foi a geometria complexa utilizada a partir do qual foram formadas estruturas auxéticas. Ensaios experimentais e estudos de simulação foram realizados nas geometrias com tipos e intensidades de gradientes diferentes para obter dados extensivos que permite inferir sobre a precisão do método.
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Кизимчук, О. П. "Розвиток наукових основ створення текстильних аукзетик-матеріалів". Thesis, 2016. https://er.knutd.edu.ua/handle/123456789/1937.

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Дисертація присвячена проблемі створення текстильних матеріалів, які мають здатність при розтягуванні збільшуватися в напрямку, перпендикулярному до прикладених сил, за рахунок будови матеріалу, а не за рахунок використання пряжі та ниток з відповідними властивостями. Виявлено геометричні структури аукзетик-матеріалів, які можуть бути реалізованими в текстильних матеріалах, зокрема трикотажних структури основов’язаного трикотажу, які виявлятимуть аукзетик-властивості, та обрані переплетення, в яких можлива реалізація таких структур. Теоретично визначено основні технологічні умови в’язання та параметри структури основов’язаних трикотажних аукзетик-матеріалів. Встановлено фактори, які впливають на коефіцієнт Пуассона основов’язаного трикотажу утоково-філейного переплетення, отримано рівняння для його визначення, в якому за основу прийнято геометричні розміри чарунки. Експериментально підтверджено правомірність застосування отриманих аналітичних рішень при виробленні матеріалів з від’ємним коефіцієнтом Пуассона. Розроблено принципи утворення сітчастих структур з гексагональними отворами чарунок та їхнє видозмінення в процесі вироблення за рахунок введення високрозтяжної нитки у вигляді повздовжнього утоку. Отримано рівняння регресії, які адекватно (з ймовірністю 0,95) описують залежності параметрів структури, розмірів чарунок та фізико-механічних властивостей трикотажу від рапорту філейного переплетення та варіанту розташування утокової нитки в структурі. Удосконалено метод дослідження коефіцієнту Пуассона з метою використання для трикотажних сітчастих матеріалів з чарунками великого розміру та розроблено експрес-метод виявлення аукзетик-здатності матеріалів.<br>Диссертация посвящена проблеме создания текстильных материалов, которые обладают способностью при растяжении увеличиваться в направлении, перпендикулярном приложенным силам, за счет структуры материала, а не за счет использования пряжи и нитей с соответствующими свойствами. В работе заложены научные основы создания текстильних аукзетик-материалов. Выявлено геометрические структуры аукзетик-материалов, которые могут быть реализованы в текстильных материалах, в частности трикотажных. Решена главная научная проблема - определены структуры основовязаного трикотажа, имеющие аукзетик-свойства, и выбраны переплетения, в которых возможна реализация таких структур. Значительное внимание в работе уделено основовязаным аукзетик-структурам с видоизмененными гексагональными ячейками, для получения которых в структуру базового филейного переплетения в качестве продольного утка вводится высокоэластичная нить. Введенный высокоэластичный компонент влияет на геометрические параметры ячеек, которые в сочетании с собственными соотношениями размеров сторон определяют отрицательное значение коэффициента Пуассона такого трикотажа. Сформулированы условия формирования ячеек гексагональной формы в трикотаже филейного переплетения. Выполнено геометрическое моделирование петель филейного трикотажа, на основании которого получены формулы для расчета длины нити в петлях разных видов, которые учитывают значения диаметра нити, высоты петли и расстояние между двумя соседними петлями ряда. В работе представлен теоретический анализ особенностей структуры трикотажа уточно-филейного переплетения, при растягивании которых коэффициент Пуассона принимает отрицательное значение. Обосновано взаимодействия уточных и грунтовых нитей в структуре филейного трикотажа в зависимости от технологических условий: взаимного расположения на машине уточных и грунтовых гребенок, их проборок, величины и направления сдвига за спинками игл. На основе математической обработки результатов исследования параметров структуры, размеров ячеек и физико-механических свойств разработанных основовязаных полотен получены уравнения регрессии, которые адекватно (с вероятностью 0,95) описывают зависимости исследуемых показателей от рапорта филейного переплетения и варианта расположения уточной нити в структуре. Основным технологическим фактором, определяющим аукзетик-свойства основовязаного трикотажа уточно-филейного переплетения, является относительное удлинение эластомерной нити перед входом в зону вязания. Предложена математическая зависимость для определения параметра, которая учитывает рапорт переплетения и размеры петель. В результате аналитических преобразований получено уравнение для определения коэффициента Пуассона основовязаных сетчастых структур, в котором за основу приняты геометрические размеры ячейки. Экспериментально подтверждена правомерность применения полученных аналитических решений при изготовлении материалов с отрицательным коэффициентом Пуассона. На основании корреляционного анализа результатов эксперимента выявлена зависимость коэффициента Пуассона аукзетик-трикотажа с видоизмененными гексагональными ячейками от таких соотношений размеров ячейки: отношение шага ячейки по вертикали к шагу ячейки по горизонтали, отношение шага ячейки по вертикали к высоте вертикальной стороны и тангенс угла наклона диагональной стороны ячейки к горизонтали. В процессе исследования размеров элементарных ячеек трикотажа, полученного чередованием в рапорте рядов трико и атласа, и аналитического расчета их соотношений показано, что лучшие аукзетик свойства достигаются в случае, когда уточная нить располагается поочередно, то на лицевой, то на изнаночной стороне трикотажа. У трикотажа, полученного чередованием в раппорте рядов трико и цепочки, лучшие аукзетик свойства достигаются в случае, когда уточная нить обвивает протяжки петель трико только одной системы нитей в одном или двух рядах. Кроме того, в результате исследований установлено, что абсолютное значение коэффициента Пуассона возрастает с увеличением количества как рядов трико, так и рядов цепочки в рапорте грунтового переплетения. В работе предложен экспресс-метод предварительной оценки аукзетик-свойств материалов и усовершенствован метод исследования коэффициента Пуассона с целью использования для трикотажных сетчатых материалов с ячейками большого размера. Разработаны технологические рекомендации для производства основовязаных аукзетик-материалов, способствующие расширению ассортимента и функциональных свойств текстильных материалов и обеспечивающие получение конкурентной продукции.<br>Doctoral dissertation devoted to the formation of textile materials, which became wider when stretched due to the structure of the material but not through the use of yarn with appropriate ability. Based on the method of system analysis and on the theoretical hypotheses, the geometric structures of auxetic materials, which can be implemented in the textiles, particularly in knitted materials, have been revealed. The main task - the creation of the warp knitted structures with auxetic-properties was solved and the selection of interlooping, which such structures can be realized in, was made. Main consideration is concentrate on the warp-knit auxetic structures with reentrant hexagonal cells. The basic principles of hexagonal cells' formation in warp knitted structures have been formulated as a result of the theoretical analysis of geometrical models of fillet interlooping. To achieve auxetic property, it is required to employ a high elastic yarn in the base structure. Introduced elastomeric component affects the geometric parameters of the cell, which in combination with ribs' length ratio define a negative value of the Poisson ratio. the length of the cell ribs is changed by the interlooping repeat (quantity of tricot and chain courses), and the angle of rib's inclination to the horizontal section is changed by the pre-tension of the elastomeric yarn and by its positioning in the structure. Analytical dependence for calculation the prior stretching of the elastomeric yarn has been obtained as a result of the geometrical modeling of auxetic warp knit structure. The equation to determine the Poisson's Ratio of warp net structures on the geometric dimensions of the cell has been determined as a result of analytical transformations, The dependencies of structural parameters, cell's size and mechanical properties of auxetic warp knit structure on the interlooping repeat and on the positioning of elastomeric yarn in the structure have been defined as result of mathematical processing of the experimental data. The method of Poisson's ratio test was improved for the purpose of testing of the mesh with large cells and the rapid method for identifying auxetic abilities of textiles was developed.
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