Fabrics having knit structures exhibiting auxetic properties and garments formed thereby

Abstract

A fabric is provided that includes a knit structure having a geometric shape imparting an auxetic property to the fabric due to rotation of one or more portions of the knit structure. In some aspects, the fabric includes a knit structure having a triangular lattice shape that imparts an auxetic property to the fabric.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates materials having positive and negative Poisson's ratios under out-of-plane bending;

FIG. 2 illustrates materials having positive and negative Poisson's ratios under in-plane tension;

FIG. 3 illustrates a typical warp knit fabric;

FIG. 4 is a micrograph of a first embodiment of a fabric according to the present disclosure in a relaxed or normal state;

FIG. 5 is a close up micrograph of a portion of the fabric of FIG. 4 having the approximate geometric knit structure of a single repeat unit superimposed thereon;

FIG. 6A illustrates the approximate geometric structure of the single repeat unit of FIG. 5 in the relaxed state;

FIG. 6B illustrates the approximate geometric structure of the single repeat unit of FIG. 5 in the deformed state;

FIG. 7A illustrates a tessellating pattern of the repeat unit of 6A;

FIG. 7B illustrates a tessellating pattern of the repeat unit of 6B;

FIG. 8 is a graph plotting changes in width and length of the fabric of FIG. 4; and

FIG. 9 is a graph plotting transverse strain data to longitudinal strain data of the fabric of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Materials that exhibit positive Poisson's ratio properties, which are discussed in detail with respect to FIGS. 1A and 2A, have been determined by the present disclosure, when used in a garment, to reduce the fit of the resultant garment.

As show in FIG. 1A, materials in ‘plate’ form generally adopt a saddle-shape curvature when exposed to out of plane bending as a result of the positive Poisson's ratio. As shown in FIG. 2A, materials having a positive Poisson's ratio, when exposed to in-plane forces, namely when placed in tension in the y-direction, contract in a direction transverse (e.g., the x-direction) to the direction of the tensile load. It has been determined by the present disclosure that fabrics exhibiting the aforementioned properties (e.g., saddle curvature and positive Poisson's contraction) can, when used to form a garment, reduce the fit of the garment.

Advantageously, the present disclosure provides fabrics having knit structures that exhibit auxetic properties. Materials having “auxetic” properties, as used herein, are those materials that have a zero or negative Poisson's ratio. An example of a material have a negative Poisson's ratio is discussed in detail with respect to FIGS. 1B and 2B.

As shown in FIG. 1B, materials having auxetic properties, when subject to out of plane bending, undergo dome-shape curvature. Accordingly, a relatively stiff garment having the auxetic knit structures of the present disclosure, when exposed to out-of-plane forces due to body movements, retains a better fit to the body as compared to those having the positive Poisson's ratio as in FIG. 1A.

As shown in FIG. 2B, materials having a negative Poisson's ratio, when exposed to in-plane forces, namely when placed in tension in the y-direction, expand in a direction transverse (e.g., the x-direction) to the direction of the tensile load. Thus, a garment having the auxetic knit structures of the present disclosure, when exposed to in-plane forces due to body movements, due to an increase in body size and/or shape, results in a concomitant Poisson's ratio-induced increase in the x-direction (when the Poisson's ratio is negative). Alternately, no increase or decrease in the x-direction results when the Poisson's ratio is zero. This expansion and/or lack of contraction retains a better fit to the body as compared to those having the positive Poisson's ratio as in FIG. 2A.

Thus, the present disclosure provides fabrics having a knit structure such that, when the used in a garment, naturally adopts to the doubly-curved human form yet also have the ability to grow or shrink in all directions simultaneously.

Without wishing to be bound to any particular theory, auxetic behavior is believed to arise due to the interplay between the geometric structure of the material and one or more mechanisms with which the geometrical structure deforms. In the classic example of auxetic behavior illustrated in FIG. 2B, the geometric structure is a re-entrant honeycomb and the mechanism with which this structure deforms is rotation or hinging of the walls or ribs of the honeycomb. The table below provides a summary of the main structures and deformation mechanisms that are believed to give rise to auxetic behavior contemplated for use in knit structures by the present disclosure.

TABLE 1
Mechanism	Geometric Structure	Example
Rotation of	Re-entrant honeycomb	Deforming by rib hinging
sub-units	Star network	Deforming by rib hinging
	Re-entrant rhombic	Deforming by rib hinging
	dodecahedron
	Triangular lattice	Deforming by rib hinging
	Corner-sharing squares	Rotating squares
	Corner-sharing	Rotating triangles
	triangles
	Ccorner-sharing	Rotating tetrahedra
	tetrahedra
Deformation	Re-entrant honeycomb	Deforming by rib flexure
of sub-units	Star network	Deforming by rib flexure
	Honeycomb	Deforming by rib stretching
	Chiral honeycomb	Deforming by rib flexure
	Corner-sharing	Deforming by dilation
	polyhedra (e.g.,
	squares, triangles,
	tetrahedra, etc)
	Triangular lattice	Deforming by rib flexure and/or
		stretching
Translation	Interlocked hexagons	Deforming by sliding of hexagons
of sub-units		with respect to one another
	Interlocked	Deforming by sliding of
	quadrilaterals	quadrilaterals with respect
		to one another
	Interlocked triangles	Deforming by sliding of
		triangles with respect
		to one another

For purposes of clarity, exemplary embodiments of fabrics having knit structures according to the present disclosure are described as warp knit fabrics. However, it should be recognized that the fabrics of the present disclosure can be any knit fabric such as, but not limited to, weft knit fabrics.

Typical warp knit fabric, as illustrated in FIG. 3, has a series of courses and a series of wales. Each course is a row of loops or stitches running across the width of the knit fabric as shown in FIG. 3A. Each wale is a column of loops or stitches running along the length (e.g., warp direction) of the knit fabric as shown in FIG. 3B.

Referring now to FIGS. 4 and 5, a first exemplary embodiment of a warp knit fabric 10 having an auxetic knit structure 12 according to the present disclosure is shown. Knit structure 12 includes loops or stitches to form a triangular lattice structure 14 (only one illustrated).

As seen from Table 1 above, triangular lattice structures are believed to exhibit auxetic properties via both the rib rotation and deformation mechanisms. Specifically, triangular lattice structures are believed to exhibit auxetic properties via rib hinging, rib flexure, rib stretching, and any combinations thereof.

For purposes of clarity, only the rib hinging mechanism of triangular lattice structure 14 is discussed in detail below with respect to FIGS. 6 and 7. Triangular lattice structure 14 has an internal angle α and an external angle β. Internal angle α is the angle between a centerline 16 and a side 18, while external angle β is the angle between the centerline and an end 20.

Under normal or relaxed conditions shown in FIGS. 6A and 7A, external angle β is between greater than about zero degrees and less than about ninety degrees. However, upon application of tension in a first direction 22 as shown in FIGS. 6B and 7B, the ends 20 of triangular lattice structure 14 hinge so that external angle β increases but remains less than about 90 degrees. In this manner, triangular lattice structure 14 deforms by hinging to expand in a second direction 24, where the second direction is about normal to the first direction 22.

Triangular lattice structure 14 is illustrated in FIG. 7 in tessellated form, namely formed into a mosaic with a plurality of the triangular lattice structures 14. Triangular lattice structure 14 in FIG. 7B having a deformed cell structure due to the application of tension 22 has undergone expansion both along the direction of the applied tension (e.g., first direction 22) and transverse to the direction of the applied tension (e.g., second direction 24) with respect to the relaxed tessellated structure in FIG. 7A. Thus, triangular lattice structure 14 is auxetic when deformation is due to the rotation of the ribs 18, 20 making up the structure.

In this illustrated embodiment, triangular lattice structure 14 is oriented so that centerline 16 is approximately normal to the warp direction.

The auxetic properties of fabric 10 were characterized using combined mechanical testing and videoextensometry.

During testing, fabric 10 was knitted on a warp knitting machine to include triangular lattice structure 14 and heat set. Fabric 10 was then cut into swaths of about 15 centimeters (cm) long by about 5 cm wide. The swaths were cut at about 45° to the warp direction.

FIG. 8 shows the width and length videoextensometry data for the fabric of FIG. 4 when subject to tensile load application along a direction that is at −45° to the warp direction. FIG. 8 shows that, as the fabric is pulled to increase in length, it expands (increases in width) and, therefore, possesses negative Poisson's ratio behavior.

The width and length data were converted to transverse and axial strains, respectively, using the definition of true strain given by:

${\varepsilon }_l=\ln \left(\frac{l}{l_0}\right)$

where ε_l is the strain, and l and l₀ are the length and original length, respectively, in the direction of interest. The Poisson's ratio v_ij which determines the change in width (along the transverse j direction) for stretching along the i direction is defined by:

$v_{\mathrm{ij}}=-\left(\frac{{\mathrm{strain}}_j}{{\mathrm{strain}}_i}\right)=-\frac{{\varepsilon }_j}{{\varepsilon }_i}$

The transverse and longitudinal strains were plotted against each other, with the slope of the resultant graph being, by definition, equal to −v_ij, where i is the direction of loading and j is the width direction. The resultant strains were plotted and are shown in FIG. 9. The data in FIG. 8 contain the derived strains for the average of all 10 transverse sections measured during the test.

Next, linear best fit lines were applied to the data set in FIG. 9, to result in a value of v₁₂=−0.20. The data from the testing supports this finding, as the data showed that fabric 10 has v₁₂=−0.22±0.03 and v₂₁=−0.13±0.02.

As seen from the example above, knit fabrics having knit structures according to the present disclosure are provided that display the auxetic (zero or negative Poisson's ratio) property.

It should be recognised that fabric 10 is discussed above by way of example where auxetic knit structure 12 is a triangular lattice structure 14. Of course, it is contemplated by the present disclosure for fabric 10 to have auxetic knit structure 12 with any structure sufficient to impart the desired auxetic property. For example, it is contemplated by the present disclosure for auxetic knit structure 12 to have a geometric shape that is selected from the group consisting of a re-entrant honeycomb, a star network, a re-entrant rhombic dodecahedron, a triangular lattice, rotating squares, rotating triangles, rotating tetrahedra, a chiral honeycomb, interlocked hexagons, interlocked quadrilaterals, interlocked triangles, and any combinations thereof.

It should also be recognised that fabric 10 is discussed above by way of example where the auxetic property is believed to be, at least in part, imparted by rib hinging. Of course, it is contemplated by the present disclosure for fabric 10 to have auxetic knit structure 12 having any structure sufficient to impart the desired auxetic property by any desired mechanism. For example, it is contemplated by the present disclosure for auxetic knit structure 12 to exhibit auxetic properties via the rotation mechanism, the deformation mechanism, the translation mechanism, and any combinations thereof. Thus, auxetic knit structure 12 can exhibit auxetic properties via rib hinging, flexure, rib stretching, and any combinations thereof.

It is contemplated by the present disclosure for fabric 10 to have yarns made of natural fibers, synthetic fibers, or combinations thereof. In some embodiments, it is contemplated by the present disclosure fabric 10 to have yarns made of auxetic fibers themselves, such as are disclosed in U.S. Pat. No. 6,878,320, the contents of which are incorporated by reference herein. In these embodiments, fabric 10 can exhibit auxetic (zero or negative Poisson's ratio) properties not only based on the knit structure, but also due to the yarn itself.

Advantageously, fabrics according to the present disclosure find use in the manufacture of garments such as, but not limited to, a brassiere, a panty, a camisole, a bathing suit, a pair of pantyhose, a leotard, a retention bandage, a support device, a compression bandage, and others. Here, fabric 10 can form a portion of the garment or can be used to form all of the garment. Fabric 10 can form all or part of various apparel garments such as: a moldable part of the garment such as, a bra cup; a figure control garment such as a foundation garment or corset; thermal-wear, where a volume of air can be trapped-in by the auxetic fabric property for insulation; and others. In addition, fabric 10 can form all or part of various medical garments such as: retention bandages; compression bandages; seamless shaped body garments for wounds suffered due to burns; and others.

Advantageously, fabrics according to the present disclosure can be knit on many commercially available circular knitting machines, which knit the fabric into a seamless tube.

It should also be recognized that the terms “first”, “second”, “third”, “upper”, “lower”, and the like may be used herein to modify various elements. These modifiers do not imply a spatial, sequential, or hierarchical order to the modified elements unless specifically stated.

While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims

1. A fabric comprising a knit structure having a geometric shape imparting an auxetic property to the fabric due to rotation of one or more portions of said knit structure.

2. The fabric as in claim 1, wherein said geometric shape imparts said auxetic property due to deformation of said one or more portions.

3. The fabric as in claim 1, wherein said geometric shape imparts said auxetic property due to translation of said one or more portions.

4. The fabric as in claim 1, wherein said geometric shape is selected from the group consisting of a re-entrant honeycomb, a star network, a re-entrant rhombic dodecahedron, a triangular lattice, rotating squares, rotating triangles, rotating tetrahedra, a chiral honeycomb, interlocked hexagons, interlocked quadrilaterals, interlocked triangles, and any combinations thereof.

5. The fabric as in claim 1, wherein the fabric is a weft knit fabric or a warp knit fabric.

6. The fabric as in claim 1, wherein the fabric comprises a seamless tube.

7. The fabric as in claim 1, wherein said knit structure comprises yarns made of a material selected from the group consisting of natural fibers, synthetic fibers, auxetic fibers, and any combinations thereof.

8. The fabric as in claim 1, wherein said auxetic property comprises a Poisson's ratio equal to zero.

9. The fabric as in claim 1, wherein said auxetic property comprises a negative Poisson's ratio.

10. A fabric comprising a knit structure having a triangular lattice shape that imparts an auxetic property to the fabric.

11. The fabric as in claim 10, wherein said auxetic property is imparted due to rotation of one or more portions of said knit structure, and/or translation of said one or more portions, and/or deformation of said one or more portions.

12. The fabric as in claim 10, wherein said knit structure comprises yarns made of a material selected from the group consisting of natural fibers, synthetic fibers, auxetic fibers, and any combinations thereof.

13. The fabric as in claim 10, wherein said auxetic property comprises a Poisson's ratio equal to zero.

14. The fabric as in claim 10, wherein said auxetic property comprises a negative Poisson's ratio.

15. A garment comprising a fabric having a knit structure that imparts an auxetic property to said fabric due to rotation of one or more portions of said knit structure.

16. The garment as in claim 15, wherein the garment comprises a garment selected from the group consisting of a brassiere, a panty, a camisole, a bathing suit, a pair of pantyhose, a leotard, a retention bandage, a support device, a compression bandage, and any combinations thereof.

17. The garment as in claim 15, wherein said knit structure imparts said auxetic property due to deformation of said one or more portions and/or due to translation of said one or more portions.

18. The garment as in claim 15, wherein said knit structure has a geometric shape selected from the group consisting of a re-entrant honeycomb, a star network, a re-entrant rhombic dodecahedron, a triangular lattice, rotating squares, rotating triangles, rotating tetrahedra, a chiral honeycomb, interlocked hexagons, interlocked quadrilaterals, interlocked triangles, and any combinations thereof.

19. The fabric as in claim 15, wherein said auxetic property comprises a Poisson's ratio of zero or less.

20. A garment comprising a fabric with a triangular lattice knit structure that imparts an auxetic property to the fabric.

21. The garment as in claim 20, wherein said knit structure comprises yarns made of a material selected from the group consisting of natural fibers, synthetic fibers, auxetic fibers, and any combinations thereof.

22. The garment as in claim 20, wherein the garment comprises a garment selected from the group consisting of a brassiere, a panty, a camisole, a bathing suit, a pair of pantyhose, a leotard, a retention bandage, a support device, a compression bandage, and any combinations thereof.

23. The garment as in claim 20, wherein said auxetic property is imparted due to rotation of one or more portions of said knit structure, and/or translation of said one or more portions, and/or deformation of said one or more portions.

24. The fabric as in claim 20, wherein said auxetic property comprises a Poisson's ratio of zero or less.