Bias yams

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. 

Braids are intertwined textile structures characterized by bias yam orientation. According to the German Industry Standard Din 60000, braids are defined as 2D or 3D fabrics with even thread density and closed fabric appearance, whose braiding threads cross each other in diagonal direction to their own edges (Wulfhorst and Gries, 2006). 

Axial Yarn A system of Axis, Crystallographic. One of several imaginary lines assumed in describing the positions of the planes by which a crystal is bounded, the positions of the atoms in the structure of the crystal and the directions associated with vectorial and tensorial physical properties longitudinal yams in a triaxial braid that are inserted between bias yams (Vincenti R (ed) (1994) Elsevier s textile dictionary. Elsevier Science and Technology Books, New York). 

Braiding Two or more yams are intertwined to form an elongated stmcture. The long direction is called the bias direction or machine direction. 

Braiding involves interlacing of a yam in what is called the bias direction. Figure... 

Three dimensional structures of multiaxial warp knitted fabrics have been recently developed for multidirectional reinforcement of composites. Multilayers of linear yams are assembled in warp (0°), weft (90°) and bias ( 0) directions to provide in-plane reinforcement in specific directions and they are stitched together by knitting yams to provide structural integrity and through the thickness reinforcement [1,2,3,4,5]. 

Skewing/bias Condition where weft yams are not square with warp yams on woven fabrics (courses are not square with wales lines on knits). 

In a manner similar to that shown for the shear-frame test, DIC can be used to capture the shear-angle contours developed in the fabric during a bias-extension test, which can be compared to the shear angles predicted by the finite element model (Fig. 6.30). It is noted that the boundaries for the three different theoretical zones as viewed in the experiment (DIC image) do not exhibit as sharp a transition as is shown for the boundaries in the simulations. The sharp transitions observed in the model are due to the pin-jointed connections between the elements whereas in reality, the yams are continuous and are allowed to bend along a smooth curve (Fig. 6.31). 

Bias Filling A fabric defect in which the filling yam does not run at a right angle to the warp. The principal cause is improper processing on the tenter frame. Also see Bow. 

The amount of inserted twist can be used to modify yam properties. Yam diameter (d) and the bias angle (a) between the nanotube orientation on the yam surface and the yam direction were measured by SEM. Typical values of d and a are 10-20 pm and 25°, respectively, for an inserted twist T of 20,000 tums/m of yam. For F ermat yams, the theoretical relationship a = tan (jtdT) is consistent with observations, despite die complex nature of the actual yam stmcture. According to the direction of twist insertion, yams are classified as S or Z yams (for clockwise and anticlockwise twist insertion, respectively). Plied yams could also be prepared simply by folding a highly twisted yam upon itself. The two yam pieces spontaneously wrap to form a stable ply. The ply twist is in the opposite direction to the yam twist, so the yam is called heterochiral (as opposed to homochiral). 

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