**3.2 Bending properties of woven fabrics**

Bending properties of fabrics govern much of their performance, such as hang and drape, and are an essential parts of complex fabric deformation analysis. The bending properties of a fabrics are determined by yarn bending behavior, the weave of the fabric and the finishing treatment of the fabric, the relationship among them are highly complex (Schwartz, 2008). Two parameters that characterize the fabric bending behavior are its bending rigidity and bending hysteresis. Bending rigidity can be defined as the resistance of textile against flexion by its specific weight and external force. Bending hysteresis can be considered as a measure of fabric's ability to recover (Pavlinić & Gerśak, 2003).

Figure 3 illustrates the typical bending curve for a woven fabric. For this curve, there are two stages with a hysteresis loop under low stress deformation. Firstly, there is an initial, higher stiffness non linear region (OA); within this region the curve shows that effective stiffness of the fabric decreases with increasing curvature from the zero motion position, as more and more of the constituent fibers are set in motion at the contact points. Secondly, a close to linear region (AB), since all the contact points are set in motion, the stiffness of the fabric seems to be close–to-constant (Schwartz, 2008).

In applications, where the fabrics are subjected to low curvature bending, such as in drapes, the hysteresis is attributed to the energy loss in overcoming the frictional forces. Under high curvature bending, the viscoelastic properties of the fibers must be considered (Schwartz, 2008).

Sensorial Comfort of Textile Materials 243

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).

Fig. 4. Stress-strain curve of woven fabric during shear deformation (Schwartz, 2008)

warp and weft threads and the structure of the fabric (Mukhopadyhay et al., 2002).

very sensitive to the pressure used in the measurement (Saville, 1999).

Fig. 5. The change in thickness with pressure (Saville, 1999)

Thickness and compressional properties of the fabric are very important characteristics in terms of fabric handle, especially for the fabrics used in garment manufacture. Fabric compressional characteristics depend on several factors like the compressional properties of the constituent

The thickness of a fabric is one of its basic properties giving information on its warmth, heaviness or stiffness in use. In practice thickness measurements are rarely used as they are

Fabric thickness is generally evaluated by measuring the distance between two parallel plates separated by a fabric sample, with a known arbitrary pressure applied and maintained between the plates (Majumdar & Saha, 2008; as cited in BS Handbook, 1974).

**3.4 Thickness and compression properties of woven fabrics** 

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