Weft direction

The stiffness of a fabric can be objectively determined as the average of the flexural rigidities (in warp and weft direction). These depend on the shear modulus and the coefficient of friction both are influenced by swelling and, therefore by humidity. 

Figure 2.6 Dependencies of mechanical properties of angle interlock reinforced composite on parameters of the reinforcement (normalised values) (a) Young s modulus in the warp direction, Ff = 58% (b) Young s modulus in the weft direction, Ff = 58% (c) shear modulus, Ff=58% (d) Young s moduli versus fibre volume fraction, PSl and PS2 refer to two values of the weft spacing.

Uniaxial tensile tests have been performed for four-ply and one-ply composites based on glass plain-weave reinforcement — Table 2.3. The composites are produced by resin infusion moulding using Dow Derakane 8084 Epoxy-Vinyl Ester resin. The weave architecmre is slightiy unbalanced exhibiting different crimp in warp and weft directions. The lay-up of four-ply composite has been balanced. 

The coating process has to deal with the special textile structure for FRC. In general non-crimped fabric structures with 0°- and 90° fiber directions are utilized. The fibers in warp- and weft direction are bonded with a knitting thread. The strength of the bond varies with the types, Tricot-and Chain-weave (... 

To determine a constant and isotropic stress rate, only a minimal surface area is required for the calculation nevertheless it is necessary to consider differing strengths in the warp and weft directions of the fabric and, to some extent, of the foil. This should preferably be taken into account in creating the cutting pattern when additional pre-stresses have to be induced in the membrane to create structural shapes which could not otherwise be developed. 

At least three samples for each load in the warp direction and three in the weft direction... 

After the pure loading tests artificial weathering tests are also required. In these weather exposure tests strips taken in the warp and weft directions are subjected to a standard climate. The exposure time is normally 1000 hours. After this time the strengths are determined. A time acceleration factor of 10 can be achieved. In other words, after 1000 hours of artificial weathering the strength loss after 10,000 hours can be determined. Alongside this are also calculation methods for the determination of the loss of... 

Coating firm, fabric manufacturer At least five in each direction, warp and weft Twenty samples in warp direction, 20 samples in weft direction for both the coating firm and the fabric manufacturer... 

Five samples in warp direction, five samples in weft direction per 1000 nf of fabric Ten samples in warp direction, 10 samples in weft direction... 

A wicking test is used to determine the absorptive velocity of water in fabrics. It is known as the capillary rise test (DIN EN 53924). With respect to time, the capillary rise of absorptive fabrics in the warp and weft directions is measured by dipping them in distilled water. The absorptive velocity depends on the capillary force, which determines the transport of liquid contrary to gravity. For fabric the wicking velocity, the path of liquid distribution and the final wet figure can be different in the warp and weft directions. 

By Unear approximation, the relationships for an orthotropic elastic material between elongations e and e and for stresses n and n in the warp and weft directions respectively are given by ... 

Roving 870 (according to DIN 18820) was used for FM3. The chosen woven fabric UD0°, 870 g/m consists of glass fibres plain woven in both warp and weft directions with edges fixed by mechanical bond glass thread. The specifications were ... 

Woven fabric 580 was used for MWl. The chosen woven fabric ST0°, 580 g/m consisted of glass roving fibres in both warp and weft directions constructed in a plain weave with edges fixed by mechanically bonded glass thread. The product specification was ... 

Staple-fibre yams - at least in the weft direction. In operation, the fabric is pulled over a series of rotating rollers termed pile and connter pile , each of which is clothed with card wire and monnted concentrically on a large cylinder of approximately 1.5 m diameter. As the cylinder rotates, the pile rollers raise the fibres proud of the surface, whereas the counter pile rollers stroke them into a more orderly fashion. Raised fabrics may comprise 100% staple-fibre yams or a combination of multifilament and staple-fibre yams, the latter being woven in satin style in which the face side is predominantly multifilament yams and the reverse side predominantly of staple-fibre yams. The smooth surface provided by the multifilaments will aid cake release, whilst the raised staple-fibre yams on the reverse side will enhance the particle collection efficiency. A significant measure of the width contraction invariably takes place during this operation and proper attention will have to be given to this when designing the fabric. 

---