Description of long-term stress relaxation in stretching oriented polymers

From an analysis of the kinetic equation for the creep rate and experimental data, an equation is proposed for stress relaxation which relates the stress σ with the time t and the temperature T: ( σ 0 σ ) m ≃ m t t 0 exp (− Q 0 kT) where σ 0 is the value of t when t→0, Q 0 is the activation of the stress relaxation process, k is the Boltzmann constant, t o is a time constant, m = α 0 σ 0/ kT, where α 0 is the activation volume when t→0. It is established experimentally that this equation gives a good description of stress relaxation arising on stretching highly oriented polymer fibres over a wide range of measurement times and temperatures.