Page 468 - Handbook of Properties of Textile and Technical Fibres

Tensile failure of polyester fibers 441

Below T g
Stress

–

Above T g

Strain
Figure 13.9 Typical tensile stress-strain curves for undrawn polyethylene terephthalate at
constant rate of deformation.
Krifa M: Fiber length distribution in cotton processing: dominant features and interaction
effects, Textil Res J 76:426e435, 2006.

extension then takes place at nearly constant load and involves thinning as the neck
travels along the fiber.
This behavior leads to difficulties during continuous drawing of fibers. When fibers
are drawn between two rollers running at different speeds (see Fig. 13.10) at temper-
atures below the glass transition (cold drawing), stable running can be achieved only
by imposing a temperature gradient on the drawing filaments between the rollers so as
to stabilize the position of the neck (Thompson, 1959). On the other hand, if drawing
takes place at temperatures above the glass transition (hot drawing), the onset of draw-
ing may be stabilized by a tension gradient imposed on the filaments by the first roller
(Smith, 1975). At intermediate temperatures, necking occurs only at high strain rates
due to the strain-rate dependence of T g . Long and Ward (1991a,b) investigated tensile

Heating (optional)
Drawing

Take up
Feed Pin ν 2

ν 1
Drawn
fiber
Undrawn
fiber
Figure 13.10 Pin drawing process.
Lotka M, Jackowski T: Yarn tension in the process of rotor spinning, AUTEX Res J, 3:23e27,
March 2003.