Weft yams

Ca.rca.ss Construction. Carcasses are made of one or more pHes of a woven fabric bonded together with an elastomeric compound. Woven materials that are used include cotton, rayon, nylon, polyester, aramids, and glass, in the pure form or in blends. The fabrics are constmcted with warp yams that mn lengthwise along the belt, and filling (weft) yams that mn crosswise. There are a variety of fabric weaves available for specific appHcations... 

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...

Fabric evidence from the earlier site, as represented by pseudo-morphs after fabric found on two copper earspools and a copper plate, is one of the simplest types of twining observed, namely, spaced twining. It can be seen on the upper surface of the earspool and on both surfaces of the plate from Mound C. Because no evidence indicated that yarn pseudomorphs had been dislodged, the original fabric structure is assumed to have consisted of spaced twining. The very nature of spaced twining requires action of the weft yams rather than those of the warp ... 

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

Polyester/wool blends are very popular, the most common blend ratios are 55 45 and 70 30 polyester wool. Polyester rich blends are normally constructed from a texturised polyester fibre warp and 55 45 polyester wool weft yams. The 20 80 polyester/wool is woven from 55 45 warp and a pure weft yam. Worsted polyester/wool blend yams may contain 2.5 - 3% solvent extractable oil, compared with 3.5- 5% for similar all wool yams. The oils have much greater affinity for polyester fibre than wool and after normal piece scouring, the blends contain residual oil content of 0.6 - 1.2% compared with 0.3% for wool. Oxidation of combing oil is influenced by exposure to light which should be avoided before scouring. Addition of surfactant to combing oil improves the scourability of the blend fabric [75]. 

Once a weave coding is defined, an analysis of the weave matrix allows answering questions about mutual positions of the yams. Consider a warp yam between two intersections with weft. Which weft yams is it interacting with in these intersections What is its position vis-a-vis these yams An answer to these questions is evident for one-layer weave, but for multilayered weaves it needs analysing the weave code. Knowing these answers allows definition of interactions between warp and weft, which is needed for building a geometrical model of the unit cell based on mechanics of these interactions, and definition of contacts between the yam needed for creation of meso-level FE models. 

Consider a warp yarn first, e.g. the first warp yam in Figure 2.2(a). Its level codes are w, = 0,2,4,2. The yarn can be subdivided into crimp intervals, which constitute a part of the yarn between two intersections. At the first crimp interval, the yarn is supported (interacts with at the ends of the interval) with weft yams in the layers (J = 1 and l = 2 (the subscript gives the number of the crimp interval, the superscript identify one of its ends). The yam is situated above its supporting weft at the left end of the crimp interval and below the supporting weft at the right end. 

To constmct the same description for a weft yam, the intersection codes and parameters of crimp intervals of warp are used. Consider a weft yarn i at layer /. First, looking up the lists of crimp interval parameters, find the first warp that has in its lists /j = 1 or... 

I (i.e. supported by the weft yarn i at layer /) This would be the left end of the first crimp interval on the weft yam. The support warp number is thus found, and the position sign of the weft would be inverse to the position sign of the warp. Then find the next warp yam supported by the weft (/,/). This would be the right end of the first crimp interval on the weft yam, and the left end of the second crimp interval. Continue until all the crimp intervals would be defined. Note that in multilayered stmctures the number of crimp intervals on a weft yarn can be smaller than the total number of the warp zones. For example, the first weft yam in the first layer of the weave. Figure 2.2(a) (eight warp zones) has only five crimp intervals, as it does not intersect with three of the Z-yams. 

With all the simplicity of the OA method it produces reasonable predictions for the fibre-dominated properties and low crimp, when deviations from the iso-strain assumption play a minor role. For off-axis properties, or for cases when transverse parts of the reinforcement (e.g. weft yams for warp-direction loading) play an important role, or in the presence of high-crimp yams (e.g. 3D reinforcements with significant fraction of binder), the iso-strain assumption is not valid any more, and quality of the OA predictions is decreased. There are approaches that combine iso-strain and iso-stress formulations [3], but these approaches leave open the choice of the combination mles open, which makes their predictive abilities limited. 

The pullout test repeated Qve times for each fabric. In the execution of the yam pullout test, a fabrie sample was clamped to each side of a U form frame. The weft yams of the fabric were free. The frame was connected to the movable lower head of a Zwick tensiometer model 1440-60 . The middle weft yam was tied to the stationary upper head while a free length at the end was set to be 1 cm. The length of the yams between the upper head and the fabric was set to be 6 cm for all samples. The lower head moved down at a velocity of 10 mm/min. The pullout force was measured by a load cell with a maximum capacity of 500 N while the pulled yam fully pulled out of the weave. 

Five plain woven fabrics, two polyester fabrics, and three cotton fabrics were examined in a yam pullout test, as schematically shown in (Figure 1(a)). Characteristics of these fabrics are presented in (Table 2). Sample PETl is consisted of twisted multi filaments of polyester as weft and warp yams. Sample PET2 has intermingled polyester multi filaments as warp and textured polyester multi filaments as weft yams. The COTl is a scoured cotton fabric with ringspun yams as wefts and warps. The COT2 is a bleached cotton fabric with ringspun weft and warp yams, and finally COTS is a bleached cotton fabric with open-end spun wefts and warps. 

The sample is clamped in a relaxed condition along the warp directiom Therefore, the warp yams are the opposed yams. The middle weft yam with a 10 mm free end was pulled in the pullout test. The pulling velocity was 10 nun/min and it kept Deed until the pulled yam left the weave completely. The pullout force was measured by a Zwick tensiometer model 1440-60 (made in Germany). The test was repeated Q e times for each fabric. 

Corrstrained yams in the fabric or other textile stractures reveal mechanical responses, which are different in compare with the free yams. Therefore, their intrinsic behavior would not be displayed perfectly. This is actually the reason of representation of Equations (13) and (15). Table 3 reveals fabric modulus along the warp direction the modiCbd warp yams modulns the spring stiffness constarrt, and the equivalent spring stiffness constant for the weft yam of each fabric. 

By producing fabrics with different components in warp and weft, it may be possible to create a stmcture that utiUses the best features of each. The most popular combinations in this respect are multifilament warp and staple-fibre weft yams (Fig. 3.24) and monofilament warp and multifilament weft yams. In both cases the ratio of warp to weft threads is at least 2 1 and usually considerably higher. This facilitates the production of fabrics with a smooth warp-faced surface for efficient cake release. 

Fig. 3.24 Scanning electron micrograph showing fabric woven with multifilament (warp) and woollen ring-spun (weft) yams.

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