Hollow fabrication

In general, a hollow woven fabric refers to one whose cross sections are porous. The materials between the two surfaces could be interlaced fabrics or simply yams and fibres. Under this definition, the hollow fabrics can be classified into hollow fabrics with uneven surfaces and those with flat surfaces. 

Figure 3.1 Illustration of a hollow fabric with uneven surfaces, (a) Fabric construction, (b) Cross section of the fabric.

Figure 3.3 shows resin-treated hollow fabrics with flat and uneven surfaces. The hollow fabric with uneven surfaces can be used in curved and flat forms, whereas the hollow fabric with flat surfaces can only be used as a board stmcture. 

Usually, hollow woven fabrics are woven with the tunnels in the weft direction. However, hollow fabric with uneven surfaces can also be made in the warp direction for applications in which long tunnel length is necessary, whereas hollow fabric with flat... 

Figure 3.4 Hollow fabric structure based on the face-to-face weaving technology.

Figure 3.5 A hollow fabric with multitunnels in multidirections.

In general terms, the woven hollow fabrics are a special type of hollow solids. Such structures have found wide use in many areas including thermal insulation, packaging, structural, and buoyancy, as well as some other applications (Gibson and Ashby, 1999). As a structural material, they have been notably used in civil engineering and aerospace engineering. 

Due the hollow construction, the volume density of the hollow composites reinforced by hollow fabrics can be very low, resulting in a type of lightweight composite material that is desirable for many applications. 

It is obvious that the volume density of the hollow composite is affected by the cell size, cell shape and cell network in the cross section as well as the open angle of the cells. The volume density of the hollow fabrics with flat surfaces can be evaluated in a similar fashion. 

Figure 3.12 Region division of a hollow structure, (a) Hollow fabric before opening.

For hexagonal hollow structures, if there are n cells in the thickness direction, then 2n layers of single layers of fabrics must be used. The adjacent layers of the 2n fabrics will be joined with and separated from one another at a predesigned pattern. Based on such specifications, a cross-sectional view of a hexagonal hollow fabric can be defined. Weaves will be assigned to the single layers as well as the joined layers. Once all these layers have received weaves respectively, all these weaves will be combined to form the overall weave for the hexagonal hollow structure based on the layer relationship. 

Figure 3.16 Final weave for the hexagonal hollow fabric.

Figure 3.17 Illustration of cross section of a quadratic hollow fabric.

Consider a three-layer quadratic structure, where A = B = 6 picks, C=D = 4picks, and Ala = 3 2 (a 48.2°). The weaves used for the top, middle and bottom fabric layers are j, j and p respectively. The weave for one repeat unit of this quadratic hollow fabric is created and is shown in Figure 3.18. 

Figure 3.18 The weave diagram created for a three-layer quadratic hollow fabric.

Possible applications of hollow fabrics and future trends... 

Use of the hollow structure in the in-plane directions offers high capacities in impact energy absorption and in impact force attenuation. This is suitable for areas where damping and protection against impact are of importance. Packaging and personal and property protection are possible areas for application. There has been work on using hollow composites reinforced by 3D hollow fabrics with uneven surfaces for limb protection against trauma impact (Yu and Chen, 2004). 

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