• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.228-233
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• 2016

Auxetic material is a material which has negative Poisson's ratio(NPR). Auxetic material shows some distinctive property like high energy absorbing property and high shear modulus. Among these, synclastic curvature is very interesting characteristic. When synclastic-curvature-material bends, it changes its shape like dome, contrary to non-auxetic material which changes its shape like saddle(anticlastic). This distinctive property could make it easy to manufacture curved structure like nose cone or wing panel in aerospace engineering. In this study, we studied a quantitative analysis about synclastic curvature of re-entrant panel with finite element model. We suggested a concept 'Degree of Synclasticity(DOS)', which means a ratio of curvature of load-direction and load-orthogonal direction. We studied the variation of DOS with two factor, unit cell inner angle(${\theta}$) and load position angle(${\phi}$). DOS decreases as ${\theta}$ increases because the unit cell goes out of auxetic-shape. As ${\phi}$ varies, DOS changes in a large range. So proper optimization of ${\phi}$ would be needed for application.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.192-197
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• 2017

Typical materials including concrete behaves with positive poisson's ratio when external force is applied. However, it is also available to manufacture a grating system which has negative poisson's ratio(Auxetic). In this study, double arrow type 2-D auxetic mesh was manufactured and mechanical behaviors were observed. Also, direct tensile tests of cementitious composites reinforced by auxetic mesh were performed and the results were compared with composites reinforced by typical mesh. The results showed that auxetic mesh more effectively restrained the deformation(shortening) of cementitious composites perpendicular to the load direction comparing with typical mesh.

• Journal of the Korean Society of Clothing and Textiles
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• v.45 no.1
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• pp.106-122
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• 2021

This study confirmed the mechanical properties of an auxetic re-entrant pattern prepared using 3D printing technology and its composite fabric with neoprene for the production of functional auxetic patterns/textiles for safety shoes. Samples were prepared by the tilt angle of a re-entrant pattern of 0°, 30°, 45°, 60° and 90°, and then analyzed using Poisson's ratio, bending, compression, and tensile properties. A 3D printed auxetic re-entrant pattern (3DP-RE) and its composite fabric (3DP-RE/NP) showed a negative Poisson's ratio in all tilting angles that indicated auxetic properties. The results of the bending property shown that strength of 3DP-RE/NP was 1.5 times lower than NP, but the strain improved 2.0 times. It was confirmed that the deformation of 3DP-RE/NP is possible with a low load. Each sample type of compression behavior indicated similar regardless of the tilting angles; in addition, the compression toughness of 3DP-RE/NP increased 1.2 times compared with NP. In the case of tensile properties, 3DP-RE and 3DP-RE/NP were affected by the tilting angle, samples with 90° (the opposite of load direction) showed best tensile property and toughness. 3DP-RE/NP indicated improved bending, compression, and tensile properties.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.198-203
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• 2017

This study observed the effects of auxetic mesh reinforcement in concrete on the mechanical characteristics under compression. Series of double arrow type 2-D auxetic mesh were manufactured and embedded into concrete specimens. Compression tests were performed and results showed that the application of auxetic mesh as concrete reinforcement can restrain the deformation of concrete resulting in the enhancement of stiffness of composites.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.116-123
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• 2017

This study has been investigated the applicability of auxetic mesh for the reinforcement of structural members. Typical materials including concrete behaves with positive poisson's ratio when external force is applied. In this study, it has been theoretically verified that metallic auxetic mesh restrains as such mechanical behaviors of concrete resulting in the stiffness increase. Also, regarding the applicability to construction field, a type of auxetic mesh has been suggested and the mechanical characteristics were numerically analyzed.

• Journal of Powder Materials
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• v.25 no.6
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• pp.507-513
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• 2018

This study investigates the viability of using a Na-ion battery with a tin(Sn) anode to mitigate the vulnerability caused by volume changes during discharge and charge cycling. In general, the volume changes of carbon material do not cause any instability during intercalation into its layer structure. Sn has a high theoretical capacity of $847mAh\;g^{-1}$. However, it expands dramatically in the discharge process by alloying Na-Sn, placing the electrode under massive internal stress, and particularly straining the binder over the elastic limit. The repeating strain results in loss of active material and its electric contact, as well as capacity decrease. This paper expands the scope of fabrication of Na-ion batteries with Sn by fabricating the binder as an auxetic structure with a unique feature: a negative Poisson ratio (NPR), which increases the resistance to internal stress in the Na-Sn alloying/de-alloying processes. Electrochemical tests and micrograph images of auxetic and common binders are used to compare dimensional and structural differences. Results show that the capacity of an auxetic-structured Sn electrode is much larger than that of a Sn electrode with a common-structured binder. Furthermore, using an auxetic structured Sn electrode, stability in discharge and charge cycling is obtained.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.317-323
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• 2017

Due to the unique characteristic of auxetic material, negative poisson's ratio, it has a variety of distinctive properties compared to conventional materials. Numerous researches have been conducted on the auxetic material in order to find out how to make auxetics. In this study, we analyzed triangular and rectangular patterned rotating rigid units using finite element method. Our purpose is to investigate the mechanical properties of the rotating rigid units and to show their auxetic behaviors. We studied the Poisson's ratio and the bulk modulus of the rotating rigid units depending on their unit cell sizes. The Poisson's ratio and the bulk modulus decreased as the number of unit cells increased. Also, when the geometry of the unit cell was changed, the tendency of the Poisson's ratio and the bulk modulus was also different from the previous case. The results of the Poisson's ratio and the bulk modulus referred that they were critically affected by the number of unit cells and the shape of unit cell.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.807-815
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• 2017

Auxetic structures with negative Poisson's ratio can be used to achieve high mechanical properties in energy absorption and destruction toughness. In this paper, we aim to design an auxetic structure which has a high negative Poisson's ratio and a stiffness over 50N/mm by using an optimization method. Length(L), thickness(t) and angle(${\theta}_1$, ${\theta}_2$) of an auxetic pyramid are the design parameters, and also stress, Poisson's ratio and stiffness are thr reaction factors. We used Box-Behnken method and conducted 4 factors - 3 levels experiment design. Finite element models are analyzed by using Edison program CSD_EPLAST.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.241-250
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• 2017

Auxetic is a structure that behave as negative Poisson's ratio. It is known for high mechanical property like energy absorption and destruction toughness so far. In this paper, we aimed to design auxetic structure which has small internal energy when force is applied and high NPR and over 50N/mm stiffness by using optimization method. We defined length(L), thickness(t), angle(${\theta}_1$, ${\theta}_2$) as design factors and also von-Mises stress, NPR, stiffness as reaction factors. We used Box-Behnken method and conducted 4factors - 3levels experiment design. We also analyzed each models by using CSD_EPLAST, Edison program, and did extra analysis for more accurate results. Finally, we found out the optimal design factors which is satisfied aimed value and increased reliability through factor analysis and validity verification.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.8
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• pp.719-724
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• 2011

A Non_Pneumatic tire (NPT) has spoke to replace air of the pneumatic tires. A NPT appears to have advantages over the conventional pneumatic tire in terms of flat proof and maintenance free. And a NPT can also be used in the space environment since it uses no air for inflation. In this study, the static contact pressure of NPTs with auxetic honeycomb spokes is investigated as a function of vertical loading and is compared with that of a pneumatic tire. The finite element based numerical simulation of the local stress of an airless tire is carried out with ABAQUS for varying vertical force and honeycomb spokes geometries.