Effect of molecular motions on time-dependent fracture

Abstract

Abstract The modification of a rate process by externally introduced conditions is well known. An equation of the same general form has been found applicable to such diverse rate phenomena as wear, friction, voltage breakdown, mechanical degradation and fracture. As applied to fracture rates, the equation takes the form, τ = τ0 exp {(E−γσ)/RT}, where T is the time to fracture, τ0 is a constant, E is an energy, γ is a stress concentration factor, σ is the applied stress, R is the gas constant, and T is the absolute temperature. This equation can only be an approximation, since it predicts a finite time to break when σ is zero. Further, although E is taken to be the energy of the breaking bond, it varies over a large range for many polymers having the same carbon backbone. In this paper, a two-position barrier model is developed, in which the barrier is that which arises from the energy for polymer chain motion. Assuming bond breaking subsequent to the rate-determining step, the stress term in the equation ...