The Stress Relaxation and Set of Wool Fibers with Particular Reference to Their Structure and Mechanical Properties-

Abstract

The stress-strain relationship of wool fibers subjected to setting treatment has been investigated using a universal tensile tester. The amount of stress relaxation of wool fibers held strained in a setting medium varies in accordance with fiber stram, but these stresses reach a constant value with respect to fiber strain at the same duration of setting, and this stress value is almost constant over a wide range of setting conditions. The stress-relaxation process may be divided by this value into two stages : the first rapid relaxation of stress may be attributable to the noncrystalline regions of wool fibers, and the second stage to the crystalline regions. It is only at the second stage that the fiber begins to acquire a set.

The significance of the constant stress value is discussed in terms of a model of wool fiber and Flory's theory of elastic mechanisms in fibrous proteins. An attempt is made to explain the stress-strain curves and the setting mechanism of wool fibers using this model and the concept of helix-random coil equilibrium of α-helices in microfibrils.