Warp and weft yams

Figure 2. Logarithm of strength retained of warp and weft yams from fabric 605 (Lot 1) as a function of heating time at 150 °C. Key O, warp A, weft.

Table III. Breaking Load of Warp and Weft Yams and Absorbance of Ninhydrin Solution Obtained from Silk...

Acid hydrolysis, regenerated cellulose, 341/ Activation energies, warp and weft yams, 68 ... 

Zhou et modified the plain woven fabrics by manufacturing honeycomb fabrics and by introducing leno structure and double weft insertions at given intervals. This serves to inaease inter-yam friction, via improved yam gripping, between the warp and weft yams. The stmctures are shown in Figs 6.5 and 6.6. It has been found that such structurally modified fabrics led to better ballistic protection than normal plain woven fabrics. 

The yams in these cloths are composed of soUd polymeric material (polypropylene, polyester, pofyamide, etc.). Cloths of diflerent patterns are produced on the loom by varying the manner in 4iidi the warp and weft yams are woven together. The warp yam is stretched in the machine or longitudinal directian and the weft yam lies at right angles to the warp. Yams are usually cylindrical, although other shapes are available. 

In the illustration shown in Figure 4.4, the plain-weave monofilament cloth has been produced by warp and weft yams of the same diam er, wovm together in a an le one-under, one-over pattern. These cloths are available in a wide range of pore azes firom 5 000 to about 30 pm, the lower limit being detennined by the abse of fibre available for the weaving process. These cloths are characterised by pores of an open type which create little flow resistance and many applications are found in areas where hi flows are required, e.g. in oil, paint, and water filtration and screening. Such cloths are readily cleaned by back-flushing. 

The warp and weft yams are positioned without being interlaced (Figure 21.13). A second set of finer warp and weft yarns binds them together, but does not contribute to the mechanical performance of the fabric. This eliminates the crimp and shear factor. 

In weaving, the warp and weft yams are commonly referred to as picks and ends. The interlacing of the picks and ends gives a coherent structure, and the repeating pattern of the interlacing is referred to as the weave of the fabric. Woven geotextiles are commonly plain weave, but twill weave and leno weave are also used. ... 

The warp and weft yams are usually specified in mass per unit length, termed the count of the yarn. In the SI system of units, the tex of a yam is used and is defined as the number of grams per 1000 m. Thus, knowing the tex of the yarns in a given fabric and the crimp ratios, the fabric areal density, Wp, can be calculated ... 

Besides flat solid fabric panels of uniform thickness, some more complex shapes have been produced and reported in the literature. For example, T-sections, 1- and L- profiles, variable thickness solid panels, and integral core stmctures with orthogonal or inclined webs (simulating box beams and tmss-like stmctures) have been demonstrated. Still, by the nature of traditional 2D weaving, where the warp and weft yam sets are mutually orthogonal in the fabric plane, the described multilayer weaving technology does not allow to introduce in-plane bias yams. 

In addition to these multiscale studies on the influence of the textile composite structure on the forming behaviour, the initial orientation of warp and weft yams of the fabric before the stamping step tends to be cracial on the resulting contour of the 3D shape as revealed in Gelin et al. (1996), mainly due to the anisotropic state of a 2D fabric. 

Due to the higher thickness value of 3D warp interlock, the exact positions of warp and weft yams, respectively, located oti the top and bottom of the 3D fabric, have to be checked during the forming process. To measure the slippage between the external layers, coloured yams have been woven on the two external surfaces of the 3D warp interlock fabric to create symmetrical and regular grids (Figure 10.12). Fifty locations have been chosen and marked vis-a-vis oti upper and bottom surfaces. 

Although the mechanical properties of constituent yams (fibres) are important for balhstic protection, the construction of fabrics can also have a significant effect on balhstic performance. Both nonwoven and woven fabric stmctures of various types with or without resin matrices have been used for ballistic applications. Typical nonwoven fabrics are felts , which are constmcted by randomly orienting and mechanically interlocking the fibres in a form of a web. In contrast, woven fabrics are constmcted through interlacing warp and weft yams. 

The enhanced ballistic performance of the 3D honeycomb fabrics may be attributed to the conjunction area between adjacent layers, which increases the yam friction in the conjunction area and the dimensional stability of the fabric as a whole. The increased yam friction in the conjimction area restrained yams from pulling out of the fabric in comparison to 2D plain woven fabric. Furthermore, both warp and weft yams in the conjunction area are better controlled with higher friction force caused by the higher yam density in the area. The reduced ballistic performance of 3D angle-interlock may be due to the difference in the number of intersections... 

The impact energy is propagated faster and in a larger area for 3D woven fabric with honeycomb structure that results from the conjunction area of the adjacent layers where the intersections of warp and weft yams are doubled, creating tighter gripping effect of the warp and weft yams in the area. 

During all these steps, various types of contacts and forces act on the warp and weft yams, and lead to their degradation as well as the change in the initial geometry of the woven stmcture (Lee et al., 2001 Abu Obaid et al., 2008). 

Figure 19.9 Schema of weaving structure with warp and weft yams [53].

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