**3.3 Shear properties of woven fabrics**

The shearing behaviour of a fabric determines its performance properties when subjected to a wide variety of complex deformations in use (Hu, 2004). The shear mechanism is one of the important properties influencing drapeness, pliability and handling of woven fabrics (Schwartz, 2008).

Shear deformation is very common during the wearing process since the fabric needs to be stretched or sheared to a greater or less degree as the body moves (Hu, 2004). This property enables fabric to undergo complex deformations and to conform to the shape of the body. The ability of a woven fabric to accept shear deformation is a necessary condition for a conformable fitting to a general three dimensional surface and is the bases for the success of woven textiles as clothing materials. This property is affected by the yarn characteristic and fabric structure (Yazdi & Ozcelik, 2007).

Shear hysteresis is defined as the force of friction occurring among interlacing points of the warp and weft yarns, when they are moving over each other, having their origin in the forces of stretching/shrinking, since the system of warp and weft yarns stretches/shrinks under strain (Pavlinić & Gerśak, 2003). Shear angle is one of the main criteria for characterizing the formability of fabrics. As the fabric is fitted onto a spatial surface, shearing occurs increasingly until the critical shearing angle is reached. When this angle exceeds a strict value, the specimen starts to buckle, i.e. wrinkling is observed (Domskienė & Strazdienė, 2005).

If a fabric is deformed at low levels of strain, the shear resistance is initial large and decreases with increasing strain (Figure 4). In this region the shear behaviour is dominated by frictional mechanism and the decreasing incremental stiffness is generally attributed to the sequential movement of frictional elements. As soon as the stress is large enough, to overcome the smallest of the frictional restraints acting at the intersection regions, the system starts to slip and the incremental stiffness falls (AB). At point B, the incremental stiffness reaches to the minimum level and remains almost linear over a range of amplitudes with slope that are called elastic elements in the fabric. At amplitudes greater than a certain amount C, the incremental stiffness again begins to rise and closed curves increase in width with increasing amplitudes of shear angle (Schwartz, 2008).

The shearing behaviour of a fabric determines its performance properties when subjected to a wide variety of complex deformations in use (Hu, 2004). The shear mechanism is one of the important properties influencing drapeness, pliability and handling of woven fabrics

Shear deformation is very common during the wearing process since the fabric needs to be stretched or sheared to a greater or less degree as the body moves (Hu, 2004). This property enables fabric to undergo complex deformations and to conform to the shape of the body. The ability of a woven fabric to accept shear deformation is a necessary condition for a conformable fitting to a general three dimensional surface and is the bases for the success of woven textiles as clothing materials. This property is affected by the yarn characteristic and

Shear hysteresis is defined as the force of friction occurring among interlacing points of the warp and weft yarns, when they are moving over each other, having their origin in the forces of stretching/shrinking, since the system of warp and weft yarns stretches/shrinks under strain (Pavlinić & Gerśak, 2003). Shear angle is one of the main criteria for characterizing the formability of fabrics. As the fabric is fitted onto a spatial surface, shearing occurs increasingly until the critical shearing angle is reached. When this angle exceeds a strict value, the specimen starts to buckle, i.e. wrinkling is observed (Domskienė &

If a fabric is deformed at low levels of strain, the shear resistance is initial large and decreases with increasing strain (Figure 4). In this region the shear behaviour is dominated by frictional mechanism and the decreasing incremental stiffness is generally attributed to the sequential movement of frictional elements. As soon as the stress is large enough, to overcome the smallest of the frictional restraints acting at the intersection regions, the system starts to slip and the incremental stiffness falls (AB). At point B, the incremental stiffness reaches to the minimum level and remains almost linear over a range of amplitudes with slope that are called elastic elements in the fabric. At amplitudes greater than a certain amount C, the incremental stiffness again begins to rise and closed curves increase in width

Fig. 3. Typical bending curve of woven fabrics (Schwartz, 2008)

**3.3 Shear properties of woven fabrics** 

fabric structure (Yazdi & Ozcelik, 2007).

with increasing amplitudes of shear angle (Schwartz, 2008).

(Schwartz, 2008).

Strazdienė, 2005).

In the case of closely woven fabrics, there is not much slippage between warp and weft yarns under shearing strain, the result being just a higher friction between individual yarns. More loosely woven fabrics, with lower cover factor, exhibit lower friction between warp and weft yarns (Pavlinić & Gerśak, 2003). Shear deformation of woven fabrics also affects the bending and tensile properties of woven fabrics in various directions rather than in the warp and weft directions only (Hu 2004; as cited in Chapman, 1980; as cited in Skelton, 1976).
