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•Deflection behaviour of existing auxetic re-entrant beams compared with traditional beam designs.•Overlooked factors of placement and orientation of auxetic clusters utilized for ...enhancement.•Two new improved auxetic beam designs proposed with minimal deflection and 64% reduction in material.•Usefulness of the proposed designs brought out by application into lightweight foot bridge design.
Auxetic materials have gained popularity in engineering applications owing to their unique deformation response mechanism. However, they have not been exploited to their full potential in engineering load bearing applications. The current paper, therefore, is focused on exploring and improving the deflection behaviour of auxetic beam structures. Initially, a single re-entrant unit cell and an array of auxetic clusters are modelled using Finite Element Method (FEM). These numerical models are then verified for its Poisson’s ratio and deflection behaviour using theoretical formulations. Subsequently, in the next phase, a comparison of the deflection characteristics of the in-use common beams with that of the conventional auxetic beam design is carried out. Much overlooked factors such as orientation and placements of auxetic clusters are introduced in beam designs and are exploited to improve the deflection characteristics of conventional auxetic beams. Through this assessment, the paper proposes two novel design concepts of Oriented Re-entrant Structures (ORS) and Assorted Re-entrant Structures (ARS) for improved load bearing response. Novel designs of ORS and ARS beams are observed to perform significantly better than the conventional auxetic and honeycomb beams. The newly proposed beam designs exhibit a 64% reduction in mass in comparison to the homogeneous beam. The usefulness of these designs are brought out by introducing the ARS auxetic beams into a real-world lightweight foot bridge design. The bridge designs with ARS cross beams demonstrates a better behaviour in comparison to the bridge designs with conventional cross beams in terms of both deformation and material usage. This work highlights the potential use of unconventional mechanical metamaterial structures in engineering load bearing problems to address the demands of green engineering and sustainability without compromising on its structural integrity.
A hierarchical octet-truss lattice material was proposed by replacing the solid strut of the octet-truss structure with a tubular re-entrant structure. The tubular re-entrant structure was ...constructed via a sheet rolling operation on a planar hexagonal re-entrant structure. Hierarchical octet-truss lattice materials with different relative densities were fabricated via additive manufacturing by adjusting the re-entrant structure rib thickness, and their mechanical properties were studied and compared with the finite element model predictions and shown to be in excellent agreement with each other. The effects of hierarchical ranks on the mechanical properties of structures were also discussed. Results showed that the Poisson’s ratio of the hierarchical octet-truss structure is approximately 0.3 without being affected by the introduction of structural hierarchy. The stress-strain relationships of the hierarchical octet-truss structures exhibit dual-peak characteristic. The lattice stiffness, compressive strength, and energy absorption capacity of the models increased with an increasing rib thickness of the re-entrant structure of the first-order hierarchical octet-truss structure, and the maximum value of specific energy absorption (SEA) was achieved when the relative density is 30.2%. The second-order hierarchical octet-truss structure exhibited lower collapse stress value, and a shorter stress plateau region than those of the zeroth and first-order hierarchical octet-truss structures.
In this paper, a new kind of chiral three-dimensional honeycomb material was designed by orthogonal assembling based on chiral two-dimensional honeycomb with four ligaments. The analytical formulae ...of equivalent Young’s modulus and Poisson’s ratio are deduced using the beam theory. The calculations of the analytical formulae can be well consistent with those of finite element method. The theoretical and numerical results show that the honeycomb material proposed in this paper is isotropic at the macroscopic scale and its Poisson’s ratio is close to −1, which means the material have larger ratio of shear modulus to Young’s modulus. Furthermore, the influence of geometries on the equivalent elastic parameters are also discussed.
•A novel 3D NPR material design method based on the tension-twist coupling effects have been proposed.•Eleven types of novel 3D lattice materials with NPR and PPR properties are proposed.•The ...numerical and experimental results show that the proposed novel 3D NPR and PPR materials exhibit desirable PR properties.
In recent years, as the development of additive manufacturing technology, 3D negative Poisson’s ratio (NPR) materials attract many researchers’ interest. In this paper, a novel 3D NPR material design method based on the tension-twist coupling effect has been proposed. A novel category of 3D NPR and positive Poisson’s ratio (PPR) materials by linking multilayer 2D NPR materials through 3D chiral chains are proposed. The sign of the Poisson’s ratio depends on the linkage pattern of the 3D chiral chain. Based on this method, 11 types of novel 3D NPR and PPR materials are presented. Experimental and numerical methods are adopted to study the mechanical properties of the proposed novel 3D NPR and PPR materials. Results show that the novel 3D materials present desirable NPR and PPR as we expected, which proved the effectiveness of the proposed design method.
•Constitutive relationship of coral concrete in different strength grades was studied.•Stress-strain curves of coral concrete in different strength grades were analysed.•Failure of coral concrete ...under uniaxial compression test was studied.•Possible applications of coral concrete in engineering structures were suggested.
The constitutive relationship of coral concrete (CPC) was researched using prismatic specimens under uniaxial compression. The equal stress cycle loading and unloading and equal strain monotonic loading methods were adopted. The elastic modulus (Ec) and Poisson’s ratio (μ) were determined. The results showed that when the specimen strain was close to the maximum, CPC was rapidly damaged in the form of splitting. The whole stress-strain curve ascent stage was composed of concave and convex curves, while the descent stage was relatively short. The ratio of residual stress (σri) and peak stress (σ0i) was 0.30–0.50, and with increase in the strength grade, σri/σ0i decreased. The two-part constitutive equations of CPC were presented, which could reflect all the characteristics of the compression tests. With increase in the strength grade, the μ of coral concrete first increased and then decreased. The Ec of CPC tended to increase. To expand the application of CPC in island engineering construction, superfine cement paste, silicon mortar, or polymer could be used to strengthen the coral surface. Adding steel bar, steel fibre, or organic fibre into CPC could also increase the CPC strength and tenacity.
Tubular auxetic structures: A review Gomes, Rafael Augusto; de Oliveira, Lucas Antonio; Francisco, Matheus Brendon ...
Thin-walled structures,
July 2023, 2023-07-00, Letnik:
188
Journal Article
Recenzirano
Auxetic materials and structures have been attracting attention due to their extraordinary mechanical properties that stand out due to their high capacity to absorb energy. Some types of auxetic ...tubular structures have been studied and designed in diverse engineering fields such as mechanical, aerospace and medical. This manuscript cites more than a hundred papers containing the definitions, designs, structural analyses and optimization, mechanical properties, and specific applications of tubular design of auxetic structures. It can be noted from the present paper that additive manufacturing has been one of the most common manufacturing techniques used in many cases to manufacture tubular structures, and numerical analysis was essential to analyzing the behavior of the structures. The purpose of this paper is to assist researchers and engineers in using the methodology step by step to develop and apply auxetic tubular structures.
•A review of auxetic tubes: definitions, optimization, properties, and applications.•Discussion about the potential applications of auxetic tubular structures.•Design and mechanical behavior of tubular auxetic structures.•Manufacturing trends of general auxetic structures and auxetic tubes.•Challenges and future directions on the auxetic tubes.
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•Multi-scale models of the punch problem of brittle auxetic/non-auxetic structures are established.•Negative Poisson’s ratio effects on the indentation resistance of cellular ...structures are evaluated.•A punch toughness concept is defined as the failure criterion of indented cellular structures.•Collinear punches problem is investigated.
This work investigates the indentation resistance of the auxetic/non-auxetic honeycomb ceramics layer by combining a discrete numerical representation and a continuum analytical model. The indentation depth of honeycombs with varying cell-wall angle and cell-wall thickness are measured. The indentation depth of auxetic honeycombs with negative Poisson’s ratio (NPR) is smaller than that of conventional ones in the premise of the same cell-wall thickness. But on the condition that the honeycombs possess the same relative density, there exists an inverse tendency. The corresponding mechanisms responsible for those trends are revealed. The stress intensity factor (SIF) is defined to characterize the stress singularity at the corner of the punch. The influence of NPR on the magnitudes of SIF is evaluated. A punch toughness concept is defined by a novel multi-scale method as the failure criterion of brittle honeycomb ceramics in indentation tests. The effects of NPR on the punch toughness of honeycombs are discussed. And the empirical formulas of punch toughness varying with the cell-wall thickness and the relative density are summarized. Finally, the NPR effects on the collinear punches problem are detected; the results show that the auxetic performance can significantly weaken the interaction between the punches.
Metamaterials with negative Poisson's ratios, showing unusual properties, are worth studying and tunability for Poisson's ratio is still a difficult problem. In this study, a 2 D/3D arc-shaped ...lattice metamaterial with tunable Poisson's ratio is designed and fabricated by additive manufacturing technology. Experimental and numerical results indicate that structures with distinct geometric features exhibit different auxetic effects, which is attributed to the deformation mode shifting from bending to stretching of the arc-shaped beams. In the bending deformation stage, the designed structure exhibits a constant negative Poisson's ratio. In the stretching deformation, Poisson's ratio begins to increase. The calculation formula of Poisson's ratio has been theoretically deduced for auxetic metamaterial and verified by experiments and simulations. The Poisson's ratio of structure can be designed by adjusting the angle of the arc-shaped ligaments. Three-dimensional (3 D) auxetic structures are designed by the periodic distribution of 2D structures horizontally and vertically, and exhibit auxetic behavior perpendicular to the loading direction. The results of 2D structures also can be applied to 3 D structures. The Poisson's ratio can also be adjusted by changing geometric parameters of 3D structures. These findings can offer new insight for the design and manufacturing of metamaterials with negative Poisson's ratio.
Stents possess disadvantages such as foreshortening and dogboning. Material selection alongside topological modifications are two main approaches to overcome these issues. Stents with negative ...Poisson's ratio, also known as auxetic property, can lead to promising performance improvement. Therefore, in this study, three stents were designed by improving a hexachiral unit cell and underwent numerical and experimental investigations using CoCr 605 L and SS 316 L alloys. The modified auxetic stents presented higher auxeticity and NPR of −0.64 and −0.69. Higher radial expansion, stress tolerance and yield strain of these modified stents help them overcome drawbacks of non-auxetic stents.
•Isogeometric shape optimization using genetic algorithm for missing rib structures with targeted deformation.•Constant negative Poisson’s ratio achieved for up till 50% effective tensile strain in ...plane stress with experimental validation.•Prescribed negative Poisson’s ratio achieved for large compressive strain emphasizing challenges in optimization and experiments under compression.
•caption: Design of missing rib auxetics with four ligaments using isogeometric genetic algorithm for prescribed constant Poisson’s ratio over large tensile and compressive strains.
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This paper presents an isogeometric shape optimization framework using genetic algorithm to design 2D auxetic structures with prescribed Poisson’s ratio over large tensile or compressive strains in the nonlinear deformation regime. The design domain is parametrized using NURBS to allow smoother shape variation of the structure and enable accurate fabrication of the optimized structures. The versatility of the framework is illustrated through the optimization of a missing rib structure with four ligaments under different loading conditions. The manufacturability of specimens using the NURBS and PolyJet 3D printing technology is also shown. The first example focuses on achieving constant negative Poisson’s ratio up to -0.7 within the applied tensile strain of 50% under plane stress condition. As auxetics experiments under large compressive strain are rarely performed and published, the second example demonstrates the optimization for compressive loading. The Poisson’s ratio determined from experiments matches well with the numerical results. The experiments highlight that for very flexible materials, deformation under self-weight and contacts between adjacent unit cells are significant factors in compression, and further investigations are needed.
