Physical Ageing and Annealing in Fibers and Textile Materials: Part I: Physical Ageing in Single Wool Fibers and Textile Assemblies

The static correspondence principle for viscoelastic composites is used to study the ageing and viscoelastic properties of the wool keratin composite and wool textile as semblies. The equilibration process of ageing before or during stress relaxation or creep tests changes the mechanical properties of the materials. In a short-term test, the ageing that occurs during the test is negligible. Increasing the ageing time of the material before mechanical testing causes a horizontal shift of the stress relaxation or creep curves in the logarithmic time scale. The effect of physical ageing on the me chanical properties of the material can therefore be represented by a single time shift factor. In a long-term test, the ageing processes that occur during the test have a pronounced influence on the mechanical properties. Therefore, the effect of ageing both before and during testing needs to be taken into account. An effective time can be used to describe the change of mechanical properties due to the ageing process. The conclusion is independent of the geometrical configuration and the stress relaxation moduli of constitutent phases. The relationship between the various ageing processes in static and dynamic tests is also discussed.