ABSTRACT
Where, n – mode of buckling, for this case the lowest mode is significant, i.e. n = 1, E – Young’s modulus, I – Moment of Inertia (I= πd4/64, d – fiber diameter), and L – effective length of fiber specimen. While Le = 0.699L and L can be assumed to be 1 mm for convenience (He et al., 2002). The critical buckling load (Fig. 7.2) of wool fibre increases exponentially with increase in average fibre diameter with R2 of 0.99 (Udakhe et al., 2011b; Bardhan et al., 2012). Fabric-evoked prickle also depends on single fiber diameter irregularities as the critical buckling load changes and thus the fiber buckling behavior (Naylor et al., 1997b). Calculation of critical buckling load using finite element method (FEM) has shown that critical buckling load reduces with increase in the fibre irregularities. Comparison of classical critical buckling and FEM of buckling has shown that agreement between these two methods is quite good, with an approximate error of only 2% (He et al., 2002).
To model the mechanics of buckling of a fiber in relation to fabric-evoked prickliness, the fiber-skin friction, the elastic stiffness, and the initial inclined angle of the fiber are introduced into the simple Euler model of buckling of a slender rod. The results demonstrated that the fiber-skin friction and the elastic stiffness have a significant effect on the buckling behavior of fiber end prickling skin and the stimulus intensity to skin (Hu et al., 2011). Reducing the buckling load of protruding fiber ends contributes to a reduction in fabric prickle, and that the fiber diameter and protruding length of fiber ends are the major factors affecting the buckling load (Mayfield, 1987). Prickle sensation is due to the level of coarse fibres present in the fabric rather than the average fibre diameter (Dollong et al., 1990). Fiber diameter distribution (coefficient of variation of diameter CVd) is a more important factor than mean fiber diameter. Knitted fabric with a mean diameter of 23.2 µm and CVd of 16.4% was less prickly than a similar fabric with a mean fiber diameter of 21.5 µm and CVd of 21.7% (Dolling et al., 1992). Fabric comfort also depends on the time of shearing as autumn shearing leads to better skin comfort due to finer ends while wide ends from spring shearing make the garments uncomfortable (Naylor et al., 1997a; Naylor et al., 2004). Prickling property of fabric varies from loom state to finished fabric as each step brings in certain variations in the fabric (Matsudaira et al., 1990). The prickle threshold mean fibre diameters for woven fabrics was considered to be about 3 µm finer than that for knitted fabrics and reducing fabric cover factor was found to be helpful for prickle reduction (Naylor et al., 1997d). Acceptability of single jersey fabric for nextto-skin wear changes rapidly from approximately 90% for 20.5 μm wool to 50% for 23.5 μm wool (Naylor et al., 1997c).
