Auxetic Tubes Research Articles

Toward enhanced mechanical rigidity: additive manufacturing of auxetic tubes with PU core and comparative analysis of unique structural behaviors

Toward enhanced mechanical rigidity: additive manufacturing of auxetic tubes with PU core and comparative analysis of unique structural behaviors

Folding Auxetic Polygonal Kirigami Tubes

Abstract Tubular auxetic structures have wide-ranging applications including medical stents, collapsible energy absorbers, and novel fasteners. To accelerate the development in these areas, and open up new application directions, an expanded range of design and construction methods for auxetic tubes is required. In this study, we propose a new method to construct polygonal cross-sectional auxetic tubes using the principles of origami and kirigami. These tubes exhibit useful global auxetic behavior under axial extension, despite the individual polygon faces not being auxetic themselves. In general, a flat kirigami sheet cannot be simply folded into a polygonal tube since this creates kinematic incompatibilities along the polygon edges. We resolve this issue by replacing the edge folds with an origami mechanism consisting of a pair of triangular facets. This approach eliminates the incompatibilities at the edges while maintaining a connection between faces. The proposed edge connection also introduces additional control parameters for the tube kinematics: for example, introducing a kinematic limit on tube extension and enabling non-uniform behavior along the length of the tube. The rich kinematic behavior possible with polygonal cross-sectional kirigami tubes has potential applications ranging from soft robotics to energy-dissipating devices.

Design optimization of reentrant auxetic tube using multiobjective Lichtenberg algorithm based on metamodelling

The authors performed the optimizations of an auxetic tube considering different structural responses: mass, critical buckling load, natural frequency, Poisson’s ratio, and maximum compression load compression. The response surface methodology was applied to generate a metamodeling with a set of non-linear equations. All data were generated via numerical modeling after experimental validation. The Lichtenberg Algorithm was used to find the best possible configurations. This paper shows something unprecedented in the literature when evaluating the static and modal performance of an auxetic tube in a multi-objective problem. The results showed an improvement of up to 43% compared to the initial model.

Experimental and numerical investigation on crashworthiness of composite reinforced auxetic cellular tubes

This study aims to investigate the crashworthiness properties of thin-walled foam-filled Auxetic metal/composite cellular tubes under quasi-static and low-velocity impact axial loading. The specimens were fabricated using thin-walled steel tubes and Glass Fiber Reinforced Composite (GFRC) laminates. The crashworthiness characteristics including peak load, absorbed energy, specific absorbed energy, and failure mechanisms of the hybrid structures were studied and compared with individual hollow section and foam-filled Auxetic tubes. In addition, detailed FE simulations were performed using LS-DYNA software, which was verified by the experiments.

Performance Optimization of Auxetic Structures on Energy Absorption of Cylindrical Sandwich Using Taguchi and ANOVA Methods

High engineering requirements of shock absorbers have increased interest in auxetic materials, which have higher specific energy absorption performance compared to conventional solid absorbers. Last decade, many optimization studies were conducted to improve the energy absorption performance of auxetic tubular structures. Most studies focused on adding inner and outer shells to thin-walled auxetic tubular absorbers with different types of lattice structures to enhance energy absorption of the cylindrical sandwiches. There are limited studies on thicker-walled auxetic tubes and their related shell thicknesses to optimize performance. In this study, the thickness of the thicker-walled auxetic core thickness (1.2 mm, 1.6 mm, 2 mm), shell thickness (16 mm, 20 mm, 24 mm), and auxetic lattice structure (Re-Entrant Circular, SiliComb, and ArrowHead) were optimized to improve the specific energy absorption of cylindrical sandwiches. The Taguchi method was used to determine the optimum parameters for cylindrical sandwiches. In addition, the effect ratio of the parameters on the specific energy absorption was investigated using the ANOVA method. The energy absorption properties of the cylindrical sandwiches were determined using the drop-weight test. The highest specific energy absorption was obtained using a shell thickness of 1.2 mm and a core thickness of 16 mm using an SiliComb lattice. It was determined that the lattice geometry was the most effective parameter on the specific energy absorption of cylindrical sandwiches, with an effect rate of 61.62%.

Experimental and numerical investigations of aluminum foam-filled auxetic circular tubular metamaterials with elliptical cells

Aluminum foam-filled circular auxetic metamaterials were designed, fabricated and investigated in this work. Firstly, the mechanical properties and deformation modes of the proposed aluminum foam-filled auxetic tubes (AFFAT) were analyzed using experimental and finite numerical methods. The load capacity of the AFFAT is larger than the sum of the load for the auxetic tube and aluminum foam. Secondly, the effect of aluminum foam’s density on the mechanical properties of AFFAT was studied. The results show that the energy contribution ratio of the interaction between the aluminum foam and auxetic tube improves with the aluminum foam’s density. Then, the effect of unit cell size on the mechanical properties of AFFAT was investigated. It can be concluded that the compression load efficiency of AFFAT with the ratio of the elliptical major axis to the minor axis increases. Finally, the study of tube type’s effect on the mechanical properties of AFFAT was carried out. Among the investigated composite structures, the AFFAT has the highest compression load efficiency. Due to their unique structural design and excellent mechanical properties, the AFFAT has great potential for applications in aerospace, vehicle crashworthiness and protective infrastructure.

Axial compression behaviour of concrete-filled auxetic tubular short columns

Concrete-filled steel columns (CFSCs) are of great interest in the literature as they are capable of carrying higher loads by combining the exceptional qualities of steel and concrete. With auxetic materials being introduced to civil engineering applications, the influence of these materials on CFSCs remains a matter of curiosity. The current study implements a nonlinear finite element analysis to evaluate the performance of circular CFSCs with six auxetic tubes under axial compression and the proposed numerical model was validated using published experimental data. The effect of the auxetic steel tube’s porosity and Poisson’s ratio on CFSCs was examined parametrically in terms of ultimate strength using the confined concrete model. Moreover, the stress distributions of the concrete and the auxetic steel tubes were also thoroughly examined. Based on the findings of the analysis, the ultimate load of CFSCs, utilising auxetic tubes with the same density and porosity but different Poisson’s ratio, increased proportionally with the increase of auxetic behaviour. When it comes to auxetic tubes with different densities and porosities, the influence of the Poisson’s ratio of the tubes diminished and the stiffness of tubes became more dominant over the mechanical characteristics of columns as the density of the auxetic steel tubes increased or decreased. The stiffness of the auxetic tubes reduced as porosity increased, as did the ultimate load of the columns. Additionally, the ultimate loads of the auxetic steel tube columns are found to be lower than those of bare steel tube columns filled with concrete due to perforations.

Lightweight auxetic tubular metamaterials: Design and mechanical characteristics

Novel auxetic tubes (NAT) were designed, fabricated and examined. Their mechanical properties were compared with the original auxetic tube (OAT) by the finite element method and experiments. The results show that NAT increases the specific energy absorption (SEA) without sacrificing the auxetic characteristic. Then, the effect of unit cell parameters on the mechanical properties of NAT tubes was explored. The results show that, in a certain range, rib reduction can improve the SEA of NAT without sacrificing the auxetic effect. To further improve the mechanical properties of NAT, three novel ribbed auxetic tubes (NRAT) were proposed and compared with NAT. It is concluded that the SEA of NAT can be improved by adding a straight rib to the inner long axis of the ellipse. In addition, the effect of straight rib width on the mechanical properties of NRAT was investigated. The results show that the larger the straight rib is, the higher the energy absorption is. Finally, the stability of the 3D auxetic tubular metamaterial is greater than that of the 2D auxetic thin-plate metamaterial by investigating. Due to their desirable mechanical properties, the NAT and NRAT have great potential for applications in medical engineering, vehicle crashworthiness and protective infrastructure.

Mechanical properties of auxetic circular and square tubes filled with aluminum foam

The incorporation of aluminum foam in auxetic tubes can significantly enhance the overall stability, stiffness and energy absorption properties. In this work, a comparative study of the mechanical properties between auxetic circular and square tubes was conducted. The foam-filled auxetic square tube (FFAST) has the best specific energy absorption (SEA) up to 1.45 among the four auxetic tubes, and exhibits a pronounced auxetic effect throughout the minor deformation under compression, with a symmetrical and stable deformation mode. The experimental and simulated results are in excellent agreement. Hence, the finite element method is subsequently applied to the parametric analysis of FFAST, including the effects of wall thickness, height and ellipticity. Firstly, it is found that the thinner the wall thickness of FFAST is, the weaker the peak force and the greater the specific energy absorption would be. Secondly, within the same minor strain of different heights, SEA remains almost the same. Finally, with the decrease in ellipticity, the yield load of the bore tube gradually grows and SEA progressively increases. It can be concluded that FFAST with the ellipticity of 1.69 has both a high SEA and non-peak force. These findings are useful for fabricating FFAST for individual scenarios of energy absorption requirements. Such composite tubular structures will have practical applications in, e.g., protective engineering, vehicle engineering and aerospace engineering.

Aluminum foam-filled auxetic double tubular structures: Design and characteristic study

In this work, a double tubular structure consisting of auxetic tubular structures and aluminum foam was proposed. The mechanical properties of the aluminum foam-filled auxetic tubular structures and aluminum foam-filled conventional tubes under uniaxial compression were compared numerically and experimentally. Compared with conventional aluminum foam-filled tubular structures (FFT), aluminum foam-filled auxetic double tubular structures (FFADT) have stable compression deformation and superior energy absorption because of stronger interaction between the aluminum foam and the auxetic tube. Although the FFADT exhibits lower bearing capacity but overcomes the shortcomings of larger peak force and larger load fluctuation that usually occurs in conventional tubes.

Mechanical characterization of a novel thickness gradient auxetic tubular structure under inclined load

A novel gradient auxetic tube is proposed, which is characterized by a gradual change in cross-section from top to bottom. Based on a verified numerical model, the mechanical properties of gradient auxetic tubular structure and traditional auxetic tubular structure under axial and inclined loads are analyzed through the finite element method. The results show that gradient auxetic tubular structures have higher overall stability, higher energy absorption and higher specific energy absorption under inclined loads. When the difference of wall thickness between the upper and lower sections of the gradient auxetic tubular structure is larger, the advantages of high energy absorption and specific energy absorption would be more prominent. Due to their excellent energy absorption properties, thickness gradient auxetic tubular structures have great potential for applications in civil engineering, vehicle crashworthiness and protective infrastructure.

Crashworthiness of a hybrid tube with an auxetic layer

Hybrid tubes of different forms have been designed and used in various sectors such as automotive, medical, pipeline, and aerospace industries for protective equipment, oesophageal stents, oil and gas pipes, and superior vibration dampers. Auxetic materials and structures have received increasing attention due to their unique properties such as negative Poisson’s ratio. They laterally expand under uniaxial tension or laterally contract under uniaxial compression. In this work, an innovative hybrid tube with an auxetic tube as the outer tube and a conventional tube as the inner tube has been investigated. All the inner tubes were made of extruded aluminum alloy 6063 with T5 heat treatment, and the outer tubes were made of stainless steel 304 and 316L with oval holes, respectively. Quasi-static compressive tests have been conducted to study the crashworthiness of such hybrid tubes. The effects of outer tube material and geometry on the deformation mode, force–displacement curve and energy absorption of hybrid tubes have been discussed. The results show that the outer auxetic tube changes the deformation of the inner tube. The load carry capacity and energy absorption of a hybrid tube increase with the strength of the outer auxetic tube.

A novel concrete-filled auxetic tube composite structure: Design and compressive characteristic study

Concrete-filled stainless steel tube (CFSST) members take advantage of the high strength and the outstanding corrosion resistance to act as an important role in civil engineering structures. However, the steel tube could not provide the perfect confinement effect for the core concrete during the initial elastic compression stage because Poisson’s ratio of the concrete is smaller than that of the stainless steel tube (SST). In this paper, a novel concrete-filled auxetic stainless steel tube (CFASST) composite structure was designed and manufactured to actively restrain the concrete, making the best use of the desirable deformation characteristics of auxetic tubular structures. The axial compressive performance of these CFASST members and their control factors were investigated experimentally and numerically. Test results were discussed in detail which included failure modes, load versus displacement curves and strain analysis. Finally, parametric analyses were conducted to further study the effects of different parameters (Poisson’s ratio, thickness of the stainless tube) on the CFSST composite structure under axial compression. It was found that CFASST composite structures possess an unusual deformation mode and an improved confinement effect.

Crushing performance of auxetic tubes under quasi-static and impact loading

Crushing performance of auxetic tubes under quasi-static and impact loading

Mechanical response of a novel hybrid tube composed of an auxetic outer layer

In this study, the deformation and energy absorption characteristics of a novel hybrid tube is investigated both experimentally and numerically. The architecture of the proposed hybrid tube composed of an inner conventional tube and a co-axially arranged outer auxetic tube. Quasi-static compressive tests were conducted on the auxetic tubes, the conventional tubes and the hybrid tubes. A three-dimensional digital image correlation technique was used to monitor the evolution of radial contraction of the tubes. Measured performance of the tubes were compared in terms of force, energy absorption, and specific energy absorption. Finite element (FE) models were also developed for the three types of tubes, analyzed using ANSYS/LS-DYNA, and validated by experimental measurements. Both experimental and numerical results showed that the presence of the auxetic tube in the hybrid tube alters the deformation mode of the conventional tube by exerting a radial force. Parametric studies were performed to investigate the effects of the outer auxetic tube, wall thickness of the inner conventional tube, the failure strain, and yield strength of the outer tube’s material on mechanical performance of the hybrid tube. Increasing the yield strength of the outer auxetic tube improved both the energy absorption and specific energy absorption characteristics of the hybrid tube significantly.

Crashworthiness analysis of cylindrical tubes with coupling effects under quasi-static axial loading: An experimental and numerical study

In most cylindrical tubes, the occurrence of negative stiffness under compression is unavoidable. This downward trend in the force–displacement relationship means a decrease in the energy-absorption capacity. To this end, this paper introduces a new assembly method comprising two concentric cylindrical tubes. The inner cylinder possesses positive Poisson's ratio behavior, whereas the outer cylinder exhibits negative Poisson's ratio behavior. When compressed, the outer and inner cylinders shrink and expand, respectively, creating surface contacts between the two cylinders, called coupling effects. This property not only avoids the occurrence of negative stiffness in outer cylindrical tube, but also increases the energy-absorption capacity in an upward trend in the force–displacement relationship. To confirm this claim, three different types of cylindrical tubes, possessing positive Poisson’s ratio, zero Poisson's ratio, and negative Poisson’s ratio behaviors, are considered. A finite-element analysis is implemented to simulate deformation patterns of cylindrical tubes. Then, to verify the results of finite-element analysis, a laser-cutting method is applied to fabricate cylindrical tubes from stainless steel tubes. The results show that the proposed assembly method increases the energy-absorption capacity by up to 95% compared to the well-known auxetic tube. Next, a parametric study is performed, in which the gap space between the two cylinders is considered as a design variable. The results reveal the smaller the gap space, the higher the energy-absorption capacity. The absorbed energy in the assembled cylinders without gap space is 17.6 J, which is 36% greater than that of cylinders with 13 mm gap space. The effects of relative density and crushing speed are also evaluated. When compared to the crushing speed, the energy-absorption capacity is highly dependent on relative density.

Mechanical properties of foam-filled auxetic circular tubes: Experimental and numerical study

In this paper, rigid polyurethane (PU) foam was filled into hollow auxetic tube for enhancing the energy absorption. The rigid PU foams and stainless-steel auxetic tube with different geometrical parameters were manufactured, respectively. They were then assembled to form composite foam-filled auxetic tube (FFAT). Four auxetic tubes and four FFATs were respectively tested to examine the enhancement of energy absorption. Tubular types and the effects of parameters including wall thickness, and ellipticity, on FFATs were analyzed numerically by using the validated models. The results show that the overall absorbed energy of FFAT is larger than the sum of single foams and hollow auxetic tube under compression. The geometrical parameters of wall thickness, ellipticity, have a considerable effect on the structural deformation mode and energy absorption. These findings could promote the applications of auxetic composite structures in protective engineering.

Compressive Property of an Auxetic-Knitted Composite Tube Under Quasi-Static Loading

Abstract This research investigates the compressive property of a novel composite based on a weft-knitted auxetic tube subjected to a quasi-static compression test. In order to maximize the influence of the fiber content on the compression test, a Kevlar yarn was used in knitting the tubular samples using three different auxetic arrow-head structures (i.e. 4 × 4, 6 × 6 and 8 × 8 structure). A quasi-static compression test was conducted under two different impact loading speeds (i.e. 5 mm/min and 15 mm/min loading speed). The results indicate that the energy absorption (EA) property of the auxetic composite is highly influenced by the auxeticity of the knitted tubular fabric.

Auxetic tubular scaffolds via melt electrowriting

Auxetics are an interesting class of materials that expand in transverse directions when tensile loading is applied. For example, in contrast to conventional materials, an auxetic tube will increase in diameter when stretched along its axis. To date, auxetic tubular scaffolds have been proposed for applications in tissue engineering and soft robotics; however, they have not yet been routinely produced in precisely-engineered microfibre structures using the melt electrowriting additive manufacturing method. Using a custom melt electrowriting device and rotating mandrel collector, scaffolds with a re-entrant honeycomb unit cell pattern were designed and fabricated from polycaprolactone microfibres. These scaffolds were tensile tested to characterise their auxetic properties compared to traditional crosshatch-patterned tubular scaffolds. The auxetic scaffolds exhibited an increase in diameter up to 80.8%, as predicted from the unit cell pattern at maximum strain of 14.1%, resulting in a Poisson's ratio of −5.8. By comparison, crosshatch scaffolds exhibited a similar stress-strain profile to the auxetic tubular scaffold with identical pore size, however significant radial compression was observed leading to a Poisson's ratio of +5.7. This study reports the design and fabrication of auxetic tubular microfibre scaffolds fabricated via melt electrowriting for the first time and offers a versatile fibre patterning system towards applications in biofabrication and robotics.

Effect of auxetic structures on crash behavior of cylindrical tube

This paper mainly concerns effects of the auxetic structure on the crash performances in terms of the axial crash force, specific energy absorption, and deceleration, which are evaluated with the conventional and honeycomb structures. Based on the systematic design procedure, the re-entrant units for the auxetic structure are regularly arranged in the tube wall, which are produced by the additive manufacturing with SUS316L metal powder. Under the low impact condition, the auxetic does not only exhibit higher specific energy absorption, but also demonstrate substantially low deceleration due to effect of the densification during the axial crash compared with the conventional tube. Furthermore, while the honeycomb tube demonstrates oscillating behavior in the deceleration, the auxetic tube tends to maintain steady deceleration after the first peak during the axial crash, which is able to guarantee enhanced damping performances under the low impact condition.