2014_Auxetic Materials and Their Potential Applications in Textiles

Original article

Auxetic materials and their potential applications in textiles

Textile Research Journal 2014, Vol. 84(15) 1600–1611 ! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/004 10.1177/00405175124490 0517512449051 51 trj.sagepub.com

Zhengyue Wang and Hong Hu

Abstract Auxetic materials are a kind of non-conventional materials having negative Poisson’s ratio. They laterally expand when stretched or laterally shrink when compressed. Compared to conventional materials, auxetic materials have a number of enhanced properties that could be very interesting for some special applications. This paper reviews the latest achievements in auxetic materials, including their properties, structures and applications. A special discussion on their potential applications in textiles is also made. It is expected that this review could provide some useful information for the future development of auxetic textile materials.

Keywords negative Poisson’s ratio, auxetic material, auxetic textiles, geometrical arrangement

Most materials exhibit a positive Poisson’s ratio, that is, they laterally shrink when stretched (Figure 1(a)) or expand exp and when com compre presse ssed d (Fig (Figure ure 1(c)). On the contrary, tra ry, aux auxeti eticc mat materi erials als exh exhibi ibitt a neg negati ative ve Poi Poisso sson’s n’s rati ra tio o (N (NPR PR), ), th that at is is,, th they ey la late tera rall lly y ex expa pand nd wh when en stretch stre tched ed (Fig (Figure ure 1(b 1(b)) )) or lat latera erally lly shr shrink ink whe when n com com-presse pre ssed d (Fig (Figure ure 1(d)). 1(d)). In the 180 1800 0 s, Voi Voigt gt1 and others had already already dis discov covere ered d the auxetic auxetic or NPR effect in somee mat som materi erials als.. At tha thatt tim time, e, aux auxetic etic materials materials were only on ly lim limite ited d to na natu tura rall ma mate teri rial alss an and d di did d no nott dr draw aw too much attention. In 1987, Lakes 2 first reported an auxetic aux etic foa foam m str struct ucture ure tha thatt cou could ld eas easily ily be man manufa ufaccture tu red d by tr tri-c i-com ompr pres essio sion n an and d he heat atin ing g pr proc oces ess. s. His work wo rk sh show owed ed th that at au auxe xetic tic ma mate teri rial alss co coul uld d al also so be obtained in a man-made way. After that, more scientists began to research auxetic materials. To date, many auxetic aux etic mat materi erials als hav havee bee been n fou found nd or man manufa ufactu ctured red 2–4 5–7 (Table (Ta ble 1) 1),, in incl clud udin ing g fo foam ams, s, composites, crys8–11 12 13 tals, metals, ceramics, etc.. For con etc conven venien ience, ce, Evans et al. 14 nam named ed thi thiss kin kind d of mat materi erial al ‘au ‘auxet xetics ics’’ in 1991, which is commonly used today. With development, auxetic materials have exceeded thee iso th isotro tropi picc an and d ma macr croo-sc scal alee lim limit it an and d ha have ve be been en extended to both the isotropic and anisotropic, ranging from macro- to nano-scales. Some large auxetic materials15–17 and molecular auxetic materials 18–21 have been

found to have good potential uses. Compared to conventio ven tional nal mat materia erials, ls, aux auxeti eticc mat materia erials ls pos posses sesss som somee enha en hanc nced ed pr prop oper ertie ties, s, su such ch as sh shea earr re resi sist stan ance ce,, 22,23 indent ind entati ation on res resista istance nce,, 24,25 syn syncla clastic stic cur curvat vature ure,,26 27 28–30 crashworthiness, sound absor absorption ption,, etc.. The etc These se enhanced enhan ced prope properties rties make the auxet auxetic ic materi materials als very attractive for many potential applications, such as personnel protection, 31 military use,32 biomedicine,26,33,34 aerospace35,36 and textile textiles. s.31,37 This paper reviews the latest research achievements in auxet auxetic ic materia materials, ls, includ including ing their prope properties, rties, structures tur es and applicati applications ons.. A spe specia ciall dis discus cussion sion on the their ir pote po tent ntia iall ap appl plica icatio tions ns in te text xtile iless is al also so ma made de.. It is expect exp ected ed tha thatt this review cou could ld pro provid videe som somee use useful ful information for the future development of auxetic textile materi materials. als.

Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong Corresponding author: Hong Hu, Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Email: [email protected]

Downloaded from trj.sagepub.com at Universidade do Minho on March 25, 2015

Wang and Hu

(a)

(b)

(c)

(d)

1601

Figure 1. Stretch/compression behavior of materials: (a)/(c) conventional materials; (b)/(d) auxetic materials.

Table 1. Some auxetic materials found or manufactured

Materials

Poisson’s ratio

Investigator

Iron pyrites PU foams Silicate a-cristobalite

–0.14 –0.70 –0.50

Love12 Lakes2 Haeri9

Zeolites –0.12 Polytetrafluoroethylene –12.00 Ultra-high molecular-weight –19.00 polyethylene Carbon fiber laminates –0.13 PP fiber –0.60 Double-helix yarn –2.10 Warp-knitted fabric –0.60 Weft-knitted fabric –0.50

Grima41 Caddock and Evans15 Alderson and Evans16 Evans et al.6 Alderson et al.57 Miller et al.61 Ugbolue et al.64 Liu et al.65

PU: polyurethane, PP: polypropylene.

Auxetic materials

measured in some directions and its NPR value was relatively high (0.5).9 The models, such as ‘rotation of rigid units’, ‘rotating rectangles’10 and ‘the rotation, dilation or concurrent rotation and dilation of the tetrahedral’,11,42,43 were proposed to explain its auxetic behavior based on the molecular framework analysis and nano-level deformation of the silicate. 10 Zeolites are another important kind of natural auxetic materials. Grima et al.44 first predicted the NPR of zeolites by using force-field-based molecular modeling. Based on the model and mechanism study, 41 the auxetic behavior of the zeolite natolite was confirmed. It was found that the zeolite natolite exhibited the NPR effect at 45 to the main crystallographic axis in the 001 plane for a value of 0.12. Natural auxetic materials are very useful and have many potential applications in sensor, molecular sieve and separation technologies. For example, zeolites are used as molecular sieves because of their availability and their well-defined molecular-sized cavities and pathways.44 

Auxetic polymers

Natural auxetic materials Naturally occurring auxetic materials have been found for more than 100 years. Today, a large number of natural auxetic materials have been discovered and investigated, including skins,38,39 ceramics,13 graphite,40 metals,12 Zeolites,41 etc. Silicate a-cristobalite, which is considered as a class of natural auxetic material, has attracted a lot of attention in recent years. The NPR effect of silicate a-cristobalite comes from the intrinsic rigid structure of the silicate. The elastic behavior of a-cristobalite was investigated by the first-principles calculations and its NPR was first found.8 Tensorial analysis of the elastic coefficients showed that the auxetic effect of a-cristobalite could be

Polyurethane (PU) foam was the first man-made auxetic polymer manufactured from the conventional open-cell PU foam by Lakes 2 in 1987 through the tricompression/heating process. The NPR value obtained was 0.7. Then, Chan and Evans 3 improved the quality of auxetic foams by dividing tri-compression into three stages, that is, only compression in one direction at each stage. This method was used to make auxetic foams with higher NPR. The highest NPR measured was 0.82. According to the elasticity theory, the NPR of isotropic materials is limited to 1, but the NPR of anisotropic materials can be very high. The auxetic polytetrafluoroethylene (PTEE),15 based on the


1602

Textile Research Journal 84(15)

particles and fibrillar microstructure, can achieve a high NPR of 12, and the auxetic ultra-high molecularweight polyethylene (UHMWPE) can even reach a higher NPR up to 19 by compaction, sintering and extrusion of the conventional UHMWPE. 16 Multisintering after compaction without the extrusion step was used to manufacture auxetic UHMWPE with improved NPR effect. Some properties of the UHMWPE made with this new method could be further enhanced compared to those of the old one. 17 It has been found that the open-cell auxetic foams with large cell size have low stiffness, which restricts their applications. To improve the stiffness, auxetic closed-cell (Figure 2) foams obtained by foaming a liquid substance or by microspheres joining were molded and studied. 4 Another method to obtain auxetics with higher stiffness was to make them at the molecular level. The poly[n]prismanes (n ¼ 36) were first identified to be auxetic at the molecular level.18 The NPR was found between .007 and 0.15. He et al.19,20 proposed a simple molecular-level approach to achieve the NPR effect, and a main chain liquid crystalline polymer was designed by a simple siteconnectivity driven rod reorientation molecular method. The NPR effect was achieved by the rod rotation from the horizontal direction to the perpendicular direction (Figure 3). Grima and Evans 21 also investigated the molecular auxetics and presented a parallel ‘graphite-like’ layers model in which each of the layers contained a planar polyphenylacetylene infinite network having a rotating-triangle structure. The possibility of nanoporomaterials with NPR by the compressiondriven self-assembly method was also discussed. The prediction model showed that the nanoporomaterials have good strength and deformation performance. 45 Auxetic polymeric materials cooperated with other properties will give a big leap in application.

Recently, Xu and Li46 manufactured a shape memory auxetic polymer based on syntactic foams through the two-dimensional (2D) stress method (stretch in one direction and compress in the transverse direction). Handjigeorgiou and Stavroulakis47 designed a smart structure that used piezoelectric actuators as the face layer and auxetic material as a core to analyze the problem of the shape control of sandwich beams. Scarpa and Smith48 coated auxetic rigid PU foam with magneto-rheological fluid to increase the electromagnetic property of the auxetic foams. These materials have multi-functions, which could be very useful in the future.

Auxetic composites Low Young’s moduli are a big problem of auxetic cellular solids, which restricts their applications.49–51 Making auxetic composites with auxetic inclusions is an effective way to enhance Young’s moduli of the auxetic materials. Milton first predicted auxetic fiber-reinforced laminates with NPR near to 1.52 After that, a number of auxetic laminates have been designed and manufactured.6 The carbon/epoxy is the preferred choice to make auxetic laminates.6 It has been found that the fatigue property of laminates is highly concerned with the fiber orientation. 53 Young’s moduli are also found to be increased by laminating the auxetic layer and aluminum alternately.54 Auxetic core structures can be used in laminated composites due to their synclastic curvature properties. The auxetic hexachiral7 truss core, trichiral honeycomb core and double arrow core 55 have been reported and their mechanical properties have been investigated. It is necessary to note that the semi-auxetic composites are also found to have properties that are not between the conventional and auxetic composites but are unique from both. 56

Auxetic textiles Auxetic textiles, including auxetic fibers, yarns and fabrics, have attracted great attention in recent years.

Figure 2. Auxetic closed-cell foams model (after Shilko and Konyok 4).

Figure 3. Site-connectivity driven rod reorientation molecular model: (a) before stretch; (b) after stretch (after He et al.20).


Wang and Hu

1603

Figure 4. (a)(b) Auxetic yarn; (c) auxetic woven fabric; (d) auxetic composite (after Miller et al.61).

Alderson et al.57 first produced the polypropylene (PP) fibers that displayed auxetic behavior using a continuous partial melt extrusion process. The NPR obtained was 0.6. After that, different auxetic fibers, such as auxetic polyester fibers 58,59 and nylon fibers, 58 were invented and developed. Compared with auxetic fibers, auxetic yarns can be realized with non-auxetic fibers using a special yarn structure. An auxetic helical yarn (Figure 4(a)) was manufactured by wrapping together two non-auxetic filaments with different stiffness60 in such a way that the stiffer filament is wrapped around the softer core filament. When stretched, the stiff filament becomes straight and the soft core filament gets wrapped around the stiff filament, as shown in Figure 4(b). This kind of auxetic yarn was used to fabricate woven fabric61 (Figure 4(c)), which could inherit the auxetic effect from the yarn. Furthermore, the composite (Figure 4(d)) reinforced with this fabric still has the auxetic behavior. Different from the fabric made from auxetic yarns, auxetic fabrics could also be manufactured from non-auxetic yarns by using special fabric structures. Most recently, knitted auxetic fabrics were manufactured using both the warp and weft-knitting technologies. Ugbolue et al. 62–64 designed several warp-knitted structures by inspiring the auxetic yarn structure (Figure 4(a)), as mentioned above. These structures were constructed from wales of chain and inlay yarns. The wales were knitted from open loops using thicker, low-stiffness filaments, and a highstiffness filament is inlaid around the underlaping loops. When stretched, the high-stiffness filament becomes straight and causes open loops to wrap around them, thus the NPR is obtained (Figure 5). Several auxetic warp-knitted fabrics were produced. The best NPR value was 0.6. Auxetic weft-knitted

Figure 5. Warp knit structures from wales of chain and inlay yarns; (after Ugbolue et al.64).

fabrics were mainly produced on electronic flat knitting machines. Various auxetic weft-knitted fabrics, developed by Liu et al. 65 and Hu et al. 66 based on different geometrical arrangements, are shown in Figure 6.

Geometry structures and models Re-entrant structures Re-entrant structures are the most commonly used auxetic structures. The first investigated re-entrant structure was a 2D re-entrant hexagon (Figure 7).67 When it is subjected to an axial extension, its diagonal


1604


Figure 6. Auxetic weft-knitted fabrics developed based on different geometrical arrangements: (a) Miura-ori pattern; (b) rotating squares; (c) re-entrant hexagons (after Hu et al.66 and Liu et al.65)

(a)

66

Figure 7. Re-entrant honeycomb structure (after Hu et al. ).

ribs will rotate to the horizontal direction, which leads to a transverse expansion of the structure. Therefore, the NPR effect is achieved. Masters and Evans 68 studied the re-entrant honeycomb by together considering the bending, stretching and hinging deformations of the honeycomb cells to derive expressions of tensile moduli, shear moduli and Poisson’s ratio. A missing rib 2D model that could better predict the NPR and stress– strain behavior of auxetic foams was proposed by Smith et al.69 The limit of the 2D model is that it can only be used to predict the in-plane behavior, and the out-of-plane behavior is completely ignored. However, auxetic materials do exist in the three-dimensional (3D) form. That implicates that the 3D model will be more accurate to predict the auxetic behavior. Lakes and Witt70 designed a tetrakaidecahedra model for foam cells. The foam cell ribs are protruding inwards compared to the conventional foam cell, and when sub jected to load, the ribs will unfold to achieve the NPR effect. Other re-entrant structures are also found to have the NPR effect. The double arrowhead 71 (Figure 8(a)) structure achieves the NPR by opening the arrowheads when stretched, while the star-shaped structure 72 (Figure 8(b)) obtains the NPR by rotating its ribs. The sinusoidal ligaments structure gets the NPR by opening up the re-entrant cells.

(b)

Figure 8. (a) Double-arrowhead; (b) star-shaped structure (after Larsen et al.71; Theocaris et al.72).

Rotating structures Rotating structures are based on the arrangement of some uniform or different size or shape units connected at the vertices. When a rotating structure is stretched, its units will rotate to open up to achieve the NPR, as shown in Figure 9. Grima and Evans 73 first found this kind of structure in inorganic crystalline materials, and then proposed rotating squares (Figure 10(a)), rotating triangles (Figure 10(b)) and rotating rectangles (Figure 10(c)). The ideal model of rotating squares with rigid units was found to be independent to the initial geometry and the loading directions, keeping the NPR at 1. So it was too simplistic to characterize the deformation of uniaxial extension. The ‘semi-rigid units’,74 ‘stretch-units’, were investigated in order to better capture the deformation characteristics of auxetic materials. The model of different-sized rigid rectangles75 was also proposed to represent the properties of different systems ranging from silicates and zeolites to liquid crystalline polymers.

Nodule and fibril structure Nodule and fibril structure was first reported by Caddock and Evans for auxetic micro-porous polymer in a 2D model (Figure 11). 15 The NPR effect comes from the nodule translation by the stretched fibrils when loaded.25 Including the out-of plan effect, the


Wang and Hu

1605

Figure 9. Rotating units open up when stretched (after Hu et al.66).

(a)

(b)

(c)

Figure 10. (a) Rotating squares; (b) rotating triangles; (c) rotating rectangles structure (after Grima et al.73).

(a)

(b)

Fibrils

Nodules

Figure 12. Chiral structure (after Grima et al.78). Figure 11. Nodule and fibril model (after Caddock and Evans15).

3D nodule and fibril model 76 could be applied to more materials, such as micro-porous expanded polymers, body-centered cubic metals and foams. Lim and Acharya77 modified the rectangle nodule to hexagonal nodule, which is approximate to sphere-like nodules for the property prediction of PP films and fibers. Investigations showed that the 3D hexagonal nodule and fibril models exhibited a greater NPR effect compared to the equivalent 2D ones.

Other structures The chiral structure (Figure 12) obtains the NPR effect by wrapping and unwrapping the ligaments around the

nodes.78 The auxetic behavior of the site-connectivity driven rod reorientation structure (Figure 3) comes from the rotation of the rods. 20,79 The rod model (Figure 13) for describing the angle-ply composites, 80 molecular rods with prismatic structure to achieve auxetic behavior at the molecular level,18 doublearrow-like ‘hard’ block and a spring-like ‘soft’ segment model for copolymers 81 was also proposed.

Properties Auxetic materials have many enhanced properties compared to conventional materials. These enhanced properties make auxetic materials very attractive for many special applications. In this part, some important properties of auxetic materials are presented.


1606


Figure 13. Angle-ply composites: (a) structure; (b) model (after Shilko et al.80).

Mechanical properties

Convenonal

Auxec

The mechanical properties of auxetic polymeric foams were systematically studied. 82,83 In general, the auxetic foams exhibit a lower Young’s modulus compared to conventional foams. The compressive Young’s modulus of auxetic foams is about half that of conventional foams in small deformation, and the same figure was found in the tensile Young’s modulus in the linear elastic deformation region. However, the shear modulus of auxetic foams is higher than conventional foams. 22,83 This property can be explained by the relations among shear modulus G, Poisson’s ratio n, Young’s modulus E and bulk modulus K . For isotropic materials, the relations are: E ¼ 2G (1 + n) ¼ 3K (1  2n). From the relations, it can be found that the Young’s modulus E of conventional materials is at least twice as high as the shear modulus G. However, for auxetic materials, as the Poisson’s ratio is negative, the shear modulus G becomes higher and the bulk modulus K becomes lower. For example, when n ¼ 1, much higher G than K can be obtained. That means the material becomes difficult to shear and easy to deform volumetrically.36

materials

materials

Figure 14. Indentation resistance.

Synclastic curvature When a conventional material is subjected to a bending force, it shows a saddle shape (Figure 15(a)) due to the perpendicular shrinkage. For an auxetic material, it demonstrates a dome shape in that the perpendicular direction has the same curve trend with the bending direction, that is, synclastic curvature (Figure 15(b)). 26 The synclastic curvature property makes an auxetic material better fitting with the curve surface, such as a dome.

Indentation resistance

Fracture toughness and crack resistance

Auxetic materials have enhanced indentation resistance compared with conventional materials. When an object is impacting on a conventional material, the material flows away (Figure 14) in the lateral directions, which causes the density reduction. On the contrary, an auxetic material flows into the vicinity of the impact point when impacting because of the NPR effect. The material becomes denser at the impact point, resulting in an increase of the indentation resistance. The auxetic UHMWPE was found to be 2.5 times the indentation resistance of conventional UHMWPE. 17 The enhanced indentation resistance has also been found in the other auxetics, for instance, auxetic fiber-reinforced composites.24,84

Auxetic materials have increased fracture toughness. The toughness of auxetic foams was investigated as a function of the permanent volumetric compression ratio.85 The toughness of auxetic foams were increased by 80%, 130% and 160% for permanent volumetric compression ratios of 2.0, 2.5, 3.0, respectively, compare to the conventional foams. The auxetic materials also have enhanced crack resistance. A crack will close up under loading due to the NPR effect.

Energy absorption properties Auxetic materials have better energy absorption properties. The cyclic compression tests on auxetic foams


Wang and Hu

(a)

(b)

Figure 15. (a) Anticlastic curvature; (b) synclastic curvature.

Convenonal materials

Tensile direcon

Tensile direcon

1607

auxetic materials are more sensitive, which allows them to be used in sensors, 92 such as hydrophones. Another usage of auxetic materials can be in aerospace applications, such as an auxetic gradient cellular core for aeroengine fan blades,35 vanes for gas turbine engines,93 thermal protection,40 aircraft nose-cones,94 wing panels,87 etc. Special auxetic materials can be used in the biomedical area,33,34 including auxetic spinal implants,95 auxetic annuloplasty prosthesis, 96 artificial blood vessels26 and auxetic esophageal stents. 97 Auxetic materials can be used as fasteners. The fastener designed by Choi and Lakes 98 is larger than the hole by a tolerance in the radial dimension. When inserted, the diameter of the fastener becomes smaller under the compressive axial force, which makes it easy to insert. When removed, the fastener laterally expands due to axial extension to resist removal. The advantage of this auxetic fastener is the simplicity of the press-fit insertion. Auxetic materials can also be used as seat cushions,99 earphones,100 etc.

Applications in textiles

Auxec materials

Figure 16. Permeability of the auxetic honeycomb.

showed the damping capacity of auxetic foams was 10 times higher than that of the original conventional foams that were used for making the auxetic foams.28,86 Sound absorption28–30 and crashworthiness27,28,30 of auxetic materials were also found to be enhanced compared to the conventional materials.

Variable permeability The auxetic materials have superior permeability compared with conventional materials, because of their pore-opening properties (Figure 16). The pores become wider in the perpendicular direction when stretched, so the pore size becomes larger in both axial and perpendicular directions. The variable permeability of the auxetic honeycomb was studied and it was found that the variable permeability could be improved from macro-scale to nano-scale.87

Applications General applications Due to their unusual properties, auxetic materials have found variable applications. 87 Auxetic materials with a pores structure can be used in the filters 88–91 because the pores open up when stretched, such as in the case of re-entrant honeycomb. Due to the low bulk modulus,

It should be pointed out that the potential applications of auxetic textiles are vast. In the fiber or yarn form, auxetics can be exploited in different ways, for example, to lock the textiles in position when a tension load is applied on a fiber-reinforced composite. 37 The fiber becomes fatter laterally when loaded and is locked into the composite, which effectively prevents the pull-out problem that often occurs in conventional fiber-reinforced composites. Another example was the auxetic blast curtains101 produced on a craft loom using the helical auxetic yarn (Figure 4(a)). The curtain opens up when the pressure wave comes. The glass fragments coming after the pressure wave can then be captured by the curtain. Therefore, the blast-proof function is achieved. Auxetic materials can be used as medical textiles. One of the examples is the smart bandage. 37 The bandage made from auxetic filaments can carry some wound-healing agent. When the bandage is applied on the swelled wound, it will open up and released the agent. When the wound heals and swelling decreases, the bandage will close and stop to release the agent, as shown in Figure 17. Auxetic fabrics can be used in protective clothing and equipment because of their good energy absorption properties and shape fitting. Protective clothing and equipment are indispensable for some dangerous sports, such as riding, racing and skating, to protect wearers from injuries by impact forces. In particular, the parts of the body, such as elbows and knees, which are easily injured, need to be protected, so that the protective pads are usually used in these areas of the


1608


Bandage applied to wound

Infected wound swells

Wound heals

Figure 17. Smart bandage (after Alderson et al.17).

protective clothing and equipment. However, the protective pads found on today’s market are mostly made from foams that have low air permeability. Threedimensional auxetic fabrics (e.g. auxetic spacer fabrics) can be used to replace foams with ones that have a better comfort property. In addition, the formation of the dome shape of auxetic fabrics under bending due to the synclastic curvature feature also makes them very easy to fit the shapes of elbows and knees and thus increases their protective performance and the freedom of movement of these body parts. The antivibration gloves31 made from auxetic PU foams have been proved to have a good anti-vibration effect by decreasing the compressive stresses. However, this kind of glove is not comfortable, and allergies could occur with long-time wearing. Like the protective clothes, using auxetic 3D fabric to replace the PU foams can be a good way to resolve this problem. Auxetic material is also a good candidate for bulletproof vest use, because the force of the bullet can be reduced by the sideways expansion of the auxetic vest.102 Using auxetic fabric to make children’s wear can be another application. Parents may know how fast their children grow up. The clothes that were just bought several months ago may get too tight and not fit their children. Many parents may buy looser clothes for their children to let them grow. However, the looser clothes may cause falls or injury when children are playing. Auxetic children’s wear can resolve this problem effectively. Auxetic fabrics made of foldable structure can easily expand in both the length and width directions, which makes the clothes be well fitted for children for a long time, so that parents do not have to frequently buy clothes for their children and can save a lot of money. It is more important that good fitting can be achieved with auxetic wear, so children do not need to wear poor-fitted clothes anymore. Maternity dresses made from auxetic fabrics can obtain a great effect. Elastic fabrics are commonly used for the belly or adjustable waist in the maternity dresses. This will cause a severe discomfort problem because more and more pressure will be applied on

the belly by elastic fabrics when the belly grows up. The use of auxetic fabrics can solve this problem. When the belly grows, the auxetic fabric becomes wider in both the waist direction and the direction perpendicular to it. In this case, the belly does not have to bear too much pressure as the auxetic fabric can naturally form a dome shape, which perfectly fits the belly shape. There are still many other potential applications of auxetic textile materials. Auxetic spacer fabrics can be used for bra cups due to their excellent shape fitting and comfortable property. Auxetic fabrics with increased air permeability under extension can be used for summer wear and functional sportswear. Auxetic yarns can be used as dental floss. The safety belts of cars can be produced with high-performance auxetic fabrics to decrease the concentration of impact pressure due to increased contact area with the human body, etc.

Challenges and perspectives The development of auxetic materials has been fast in recent years. A large number of auxetic materials have been discovered, made or investigated, including fibers, yarn, fabrics, foams, composites, metals, ceramics, etc. Although many potential applications have been proposed, real applications of auxetic materials are still limited at the primary stage. The work in the future should make more effort on the development of new auxetic materials that have real applications. The combination of auxetic effect with other functions, such as shape memory and electromagnetic effect to make multi-functional auxetic materials, should be taken into consideration to upgrade material properties and usages. The extension of auxetic materials to more field applications, such as textiles, aerospace or biomedicine, should be a future trend. To date, only a few auxetic fabrics have been developed and they have not been very suitable for apparel use yet. The design and manufacture of auxetic fabrics with non-auxetic yarns still remains a great challenge for textile specialists. Further systematic studies of


Wang and Hu auxetic fabrics should be carried out in order to fully exploit this new kind of material based on textile technology. The most important factor that needs to be improved is to make auxetic fabrics keep their auxetic effect during repeating uses. More effort should be made to develop auxetic fabrics with better wearability. Three-dimensional auxetic fabrics to replace foam pads used in protective clothing need further development. Smart textiles incorporated with auxetic behavior could be a good choice for the further development of auxetic textiles. For example, anti-bacteria clothes with auxetic behavior can open up pores to release the drug when put on, and close the pore when taken off by using the variable permeability properties of auxetic materials. With the effort of researchers, it is believed that more auxetic textile materials will successfully be developed for a large number of applications in the future. Funding This work was supported by the Research Grants Council of the Hong Kong Special Administrative Region Government (grant number PolyU5165/10E).

References 1. Voigt W. Bestimmung der Elasticita ¨tsconstanten fu ¨r das chlorsaure Natron. Annalen der Physik und Chemie 1893; 49: 719–723. 2. Lakes RS. Foam structures with a negative Poisson’s ratio. Science 1987; 235: 1038–1040. 3. Chan N and Evans KE. Fabrication methods for auxetic foams. J Mater Sci 1997; 32: 5945–5953. 4. Shilko S and Konyok D. Numerical and experimental study of auxetic closed-cell foams. Comput Methods Sci Technol 2004; 10: 197–202. 5. Topolov VY and Bowen CR. Characteristics of 1–3 type ferroelectric ceramic/auxetic polymer composite. Model Simul Mater Sci 2008; 16: 015007. 6. Evans KE, Donoghue JP and Alderson KL. The design, matching and manufacture of auxetic carbon fibre laminates. J Compos Mater 2004; 38: 95–106. 7. Cicala G, Recca G, Oliveri L, et al. Auxetic hexachiral truss core reinforced with twisted hemp yarns: out of plane shear properties. In: 16th international conference on composite structures (ICCS 16), 2011. 8. Nitin RK and James RC. Negative Poisson ratios in crystalline SiO2 from first-principles calculations. Nature 1992; 358: 222–224. 9. Haeri AY, Weidner DJ and Parise JB. Elasticity of a-cristobalite: a silicon dioxide with a negative Poisson’s ratio. Science 1992; 257: 650–652. 10. Grima JN, Gatt R, Alderson A, et al. An alternative explanation for the negative Poisson’s ratios in a-cristobalite. Mater Sci Eng A Struct 2006; 423: 219–224. 11. Alderson A and Evans KE. Deformation mechanisms leading to auxetic behaviour in the a-cristobalite and aquartz structures of both silica and Germania. J Phys Condens Mater 2009; 21: 025401.

1609

12. Love AEH. A treatise on the mathematical theory of elasticity, 4th edn. New York: Dover Publications, 1944. 13. Ledbetter H and Lei M. Monocrystal elastic constants of orthotropic Y1Ba2Cu3O7: an estimate. J Mater Res 1991; 6: 2253–2255. 14. Evans KE, Nkansah MA, Hutchinson IJ, et al. Molecular network design. Nature 1991; 353: 124. 15. Caddock BD and Evans KE. Microporous materials with negative Poisson’s ratios. I. Microstructure and mechanical properties. J Phys D Appl Phys 1989; 22: 1877–1882. 16. Alderson KL and Evans KE. The fabrication of microporous polyethylene having a negative Poisson’s ratio. Polymer 1992; 33: 4435–4438. 17. Alderson KL, Webber RS, Kettle AP, et al. Novel fabrication route for auxetic polyethylene. Part 1. Processing and microstructure. Polym Eng Sci 2005; 45: 568. 18. Pour N, Itzhaki L, Hoz B, et al. Auxetics at the molecular level: a negative Poisson’s ratio in molecular rods. Angew Chem 2006; 118: 6127–6129. 19. He C, Liu P, McMullan PJ, et al. Toward molecular auxetics: main chain liquid crystalline polymers consisting of laterally attached para-quaterphenyls. Phys Stat Sol B 2005; 242: 576–584. 20. He C, Liu P and Griffin AC. Toward negative Poisson ratio polymers through molecular design. Macromolecules 1998; 31: 3145–3147. 21. Grima JN and Evans KE. Self expanding molecular networks. Chem Commun 2000; 16: 1531–1532. 22. Scarpa F and Tomlin PJ. On the transverse shear modulus of negative Poisson’s ratio honeycomb structures. Fatigue Fract Eng M 2000; 23: 717–720. 23. Ju J and Summers JD. Hyperelastic constitutive modeling of hexagonal honeycombs subjected to in-plane shear loading. J Eng Mater Technol 2011; 133: 011005. 24. Coenen VL and Alderson KL. Mechanisms of failure in the static indentation resistance of auxetic carbon fibre laminates. Phys Stat Sol B 2011; 248: 66–72. 25. Alderson KL, Fitzgerald A and Evans KE. The strain dependent indentation resilience of auxetic microporous polyethylene. J Mater Sci 2000; 35: 4039–4047. 26. Evans KE and Alderson A. Auxetic materials: functional materials and structures from lateral thinking! Adv Mater 2000; 12: 617–628. 27. Scarpa F, Yates JR, Ciffo LG, et al. Dynamic crushing of auxetic open-cell polyurethane foam. P I Mech Eng C-J Mech 2002; 216: 1153–1156. 28. Scarpa F, Ciffo LG and Yates JR. Dynamic properties of high structural integrity auxetic open cell foam. Smart Mater Struct 2004; 13: 49–56. 29. Scarpa F, Bullough WA and Lumley P. Trends in acoustic properties of iron particle seeded auxetic polyurethane foam. P I Mech Eng C-J Mech 2004; 218: 241–244. 30. Scarpa F and Smith FC. Passive and MR fluidcoated auxetic PU foam mechanical, acoustic, and electromagnetic properties. J Intel Mater Syst Str 2004; 15: 973–979. 31. Scarpa F, Giacomin J, Zhang Y, et al. Mechanical performance of auxetic polyurethane foam for antivibration glove applications. Cell. Polym 2005; 24: 253–268.


1610


32. Ma ZD, Liu YY, Liu XM, et al. Ultralightweight runflat tires based upon negative Poisson ratio (NPR) auxetic structures. Patent 2011/0168313A1, USA, 2011. 33. Dolla W, Fricke BA and Becker BR. Structural and drug diffusion models of conventional and auxetic drugeluting stents. J Med Devices 2007; 1: 47–56. 34. Scarpa F. Auxetic materials for bioprostheses. IEEE Signal Processing Mag 2008; 25: 126–128. 35. Lira C, Scarpa F and Rajasekaran R. A gradient cellular core for aeroengine fan blades based on auxetic configurations. J Intel Mater Syst Str 2011; 22: 907–917. 36. Liu Q. Literature review: materials with negative Poisson’s ratios and potential applications to aerospace and defence. DSTO-GD-0472, DSTO Formal Reports, 2006. 37. Alderson A and Alderson K. Expanding materials and applications: exploiting auxetic textiles. Tech Text Int 2005; 14: 29–34. 38. Lees C, Vincent JFV and Hillerton JE. Poisson’s ratio in skin. Biomed Mater Eng 1991; 1: 19–23. 39. Veronda DR and Westmann RA. Mechanical characterization of skin-finite deformations. J Biomech 1970; 3: 111–124. 40. Garber AM. Pyrolytic materials for thermal protection systems. Aerospace Eng 1963; 22: 126–137. 41. Grima JN, Gatt R, Zammit V, et al. Natrolite: a zeolite with negative Poisson’s ratios. J Appl Phys 2007; 101: 086102. 42. Alderson A, Alderson KL, Evans KE, et al. Modelling the deformation mechanisms, structure–property relationships and applications of auxetic nanomaterials. Phys Stat Sol B 2005; 242: 499–508. 43. Alderson A and Evans KE. Molecular origin of auxetic behavior in tetrahedral framework silicates. Phys Rev Lett 2002; 89: 225503. 44. Grima JN, Jackson R, Alderson A, et al. Do zeolites have negative Poisson’s ratios? Adv Mater 2000; 12: 1912–1918. 45. Shilko SV, Petrokovets EM and Pleskachevsky YM. Prediction of auxetic phenomena in nanoporomaterials. Phys Stat Sol B 2008; 245: 2445–2453. 46. Xu T and Li G. A shape memory polymer based syntactic foam with negative Poisson’s ratio. Mater Sci Eng A 2011; 528: 6804–6811. 47. Hadjigeorgiou EP and Stavroulakis GE. The use of auxetic materials in smart structures. Comput Methods Sci Technol 2004; 10: 147–160. 48. Scarpa F and Smith FC. Passive and MR fluidcoated auxetic PU foam – mechanical, acoustic, and electromagnetic properties. J Intel Mater Syst Str 2004; 15: 973–979. 49. Gibson LJ, Ashby MF, Schajer GS, et al. The mechanics of two-dimensional cellular materials. Proc R Soc Lond A 1982; 382: 25–42. 50. Wei GY and Edwards SF. Polymer network with negative Poisson’s ratios. Comput Theoret Polym Sci 1992; 2: 44–54. 51. Boal DH, Seifert U and Shillcock JC. Negative Poisson ratio in two-dimensional networks under tension. Phys Rev E 1993; 48: 4274–4283.

52. Milton GW. Composite materials with Poisson’s ratios close to 1. J Mech Phys Solids 1992; 40: 1105–1137. 53. Bezazi A, Boukharouba W and Scarpa F. Mechanical properties of auxetic carbon/epoxy composites: static and cyclic fatigue behavior. Phys Stat Sol B 2009; 246: 2102–2110. 54. Donesc S, Chiroiu V and Munteanu L. On the Young’s modulus of an auxetic composite structure. Mech Res Commun 2009; 36: 294–301. 55. Alderson A, Alderson KL and Ravirala N. Design and modeling of mechanical and thermal responses of novel auxetic honeycomb cores for structural composites. In: 16th international conference on composite structures (ICCS 16), 2011. 56. Lim TC and Acharya UR. Counterintuitive modulus from semi-auxetic laminates. Phys Stat Sol B 2011; 248: 60–65. 57. Alderson KL, Alderson A, Smart G, et al. Auxetic polypropylene fibres: Part 1- manufacture and characterization. Plast Rubber Compos 2002; 31: 344–349. 58. Ravirala N, Alderson A, Alderson KL, et al. Expanding the range of auxetic polymeric products using a novel melt-spinning route. Phys Stat Sol B 2005; 242: 653–664. 59. Ravirala N, Alderson KL, Davies PJ, et al. Negative Poisson’s ratio polyester fibers. Text Res J 2006; 76: 540–546. 60. Hook PB, Evans KE, Hannington JP, et al. Moisture sensitive auxetic material . Patent KR20060009826, KR, 2006. 61. Miller W, Hook PB, Smith CW, et al. The manufacture and characterisation of a novel, low modulus, negative Poisson’s ratio composite. Compos Sci Technol 2009; 69: 651–655. 62. Ugbolue SC, Warner SB, Kim YK, et al. The formation and performance of auxetic textiles. NTC Project F06MD09: Annual Report, 2006. 63. Ugbolue SC, Warner SB, Kim YK, et al. The formation and performance of auxetic textiles. NTC Project F06MD09: Annual Report, 2007. 64. Ugbolue SC, Kim YK, Warner SB, et al. The formation and performance of auxetic textiles. Part I: Theoretical and technical considerations. J Text Inst 2010; 101: 660–667. 65. Liu YP, Hu H, Lam JKC, et al. Negative Poisson’s ratio weft-knitted fabrics. Text Res J 2010; 80: 856–863. 66. Hu H, Wang ZY and Liu S. Development of auxetic fabrics using flat knitting technology. Text Res J 2011; 81: 1493–1502. 67. Evans KE, Alderson A and Christian FR. Auxetic twodimensional polymer networks an example of tailoring geometry for specific mechanical properties. J Chem Soc Faraday Trans 1995; 91: 2671–2680. 68. Masters IG and Evans KE. Models for the elastic deformation of honeycombs. Compos Struct 1996; 35: 403–422. 69. Smith CW, Grima JN and Evans KE. A novel mechanism for generating auxetic behavior in reticulated foams: missing rib foam model. Acta Mater 2000; 48: 4349–4356.


Wang and Hu 70. Lakes RS and Witt R. Making and characterizing negative Poisson’s ratio materials. Int J Mech Eng Educ 2000; 30: 50–58. 71. Larsen UD, Sigmund O and Bouwstra S. Design and fabrication of compliant mechanisms and material structures with negative Poisson’s ratio. J MicroElectroMech S 1997; 365–371. 72. Theocaris PS, Stavroulakis GE and Panagiotopoulos PD. Negative Poisson’s ratios in composites with star-shaped inclusions: a numerical homogenization approach. Arch Appl Mech 1997; 67: 274–286. 73. Grima JN and Evans KE. Auxetic behavior from rotating squares. J Mater Sci Lett 2000; 19: 1563–1565. 74. Grima JN, Zammit V, Gatt R, et al. Auxetic behaviour from rotating semi-rigid units. Phys Status Solibi B 2007; 244: 866–882. 75. Grima JN, Manicaro E and Attard D. Auxetic behaviour from connected different-sized squares and rectangles. Proc R Soc A 2011; 467: 439–458. 76. Gaspar N, Smith CW, Alderson A, et al. A generalised three-dimensional tethered-nodule model for auxetic materials. J Mater Sci 2011; 46: 372–384. 77. Lim TC and Acharya RU. An hexagonal array of fourfold interconnected hexagonal nodules for modeling auxetic microporous polymers: a comparison of 2D and 3D models. J Mater Sci 2009; 44: 4491–4494. 78. Grima JN, Gatt R and Farrugia PS. On the properties of auxetic meta-tetrachiral structures. Phys Stat Sol B 2008; 245: 511–520. 79. Griffin AC, Kumar S and McMullan PJ. Textile fibers engineered from molecular auxetic polymers. M04-GT21, NTC Project, 2004. 80. Shilko SV, Petrokovets EM and Pleskachevsky YM. Peculiarities of friction in auxetic composites. Phys Stat Sol B 2008; 245: 591–597. 81. Wei GY. Design of auxetic polymer self-assemblies. Phys Stat Sol B 2005; 242: 742–748. 82. Chan N and Evans KE. The mechanical properties of conventional and auxetic foams Part I: compression and tension. J Cell Plast 1999; 35: 130–165. 83. Chan N and Evans KE. The mechanical properties of conventional and auxetic foams Part II: shear. J Cell Plast 1999; 35: 166–183. 84. Alderson KL, Simkins VR, Coenen VL, et al. How to make auxetic fibre reinforced composites. Phys Stat Sol B 2005; 242: 509–518. 85. Choi JB and Lakes RS. Fracture toughness of reentrant foam materials with a negative Poisson’s ratio: experiment and analysis. Int J Fracture 1996; 80: 73–83. 86. Scarpa F, Giacomin JA, Bezazi A, et al. Dynamic behavior and damping capacity of auxetic foam pads. In: proceedings of smart structures and materials conference San Diego, CA. 2006, p.6169.

1611

87. Prawoto Y. Seeing auxetic materials from the mechanics point of view: a structural review on the negative Poisson’s ratio. Compos Mater Sci 2012; 58: 140–153. 88. Rasburn J, Mullarkey PG, Evans KE, et al. Auxetic structures for variable permeability systems. Aiche J 2001; 47: 2623–2626. 89. Alderson A, Rasburn J and Evans KE. Mass transport properties of auxetic (negative Poisson’s ratio) foams. Phys Stat Sol B 2007; 244: 817–827. 90. Alderson A, Rasburn J, Ameer-Beg S, et al. An auxetic filter: a tuneable filter displaying enhanced size selectivity or defouling properties. Ind Eng Chem Res 2000; 39: 654–665. 91. Alderson A, Rasburn J, Evans KE, et al. Auxetic polymeric filters display enhanced de-fouling and pressure compensation properties. Membr Technol 1994; 2001: 6–8. 92. Smith WA and Vienna V. Composite piezoelectrics utilizing a negative Poisson’s ratio polymer. Patent US5334903, USA, 1994. 93. Nakamura M. Fundamental properties of intermetallic compounds. Mater Res Soc Bull 1995; 8: 33–39. 94. Evans KE. Tailoring the negative Poisson’s ratio. Chem Ind 1990; 20: 654. 95. Baker CE. Auxetic spinal implants: consideration of negative Poisson’s ratio in the design of an artificial intervertebral disc. Master’s Thesis, 2011. 96. Burriesci G and Bergamasco G. Annuloplasty prosthesis with an auxetic structure. Patent US8034103B2, USA,2011. 97. Ali MN and Rehman IU. An auxetic structure configured as oesophageal stent with potential to be used for palliative treatment of oesophageal cancer; development and in vitro mechanical analysis. J Mater Sci Mater Med 2011; 22: 2573–2581. 98. Choi JB and Lakes RS. Design of a fastener based on negative Poisson’s ratio foam. Cell Poly1991; 10: 205–212. 99. Loureiro MA and Lakes RS. Scale-up of transformation of negative Poisson’s ratio foam: slabs. Cell Poly 1997; 16: 349–363. 100. Jones O. Cushioned earphones. Patent US6412593B1, USA, 2002. 101. Engineering and Physical Sciences Research Council. Expanding blast-proof curtain will reduce impact of bomb explosions, http://www.epsrc.ac.uk/newsevents/ news/2010/Pages/blastproofcurtain.aspx (2010). Accessed: February 10, 2012. 102. Nagai K. Narrow passage moving body structure. Patent JP06137799, Japan, 1994.


2014_Auxetic Materials and Their Potential Applications in Textiles

Recommend Documents