Dependence of craze velocity on stress and on the absorption and diffusion of environmental gases

Abstract

Abstract A comprehensive equation for the velocity of a craze in an environmental gas was obtained in terms of the stress, temperature, and partial pressure of the gas. The physical parameters of the gas that enter the equation are boiling point, heat of vaporization and diffusion coefficient. The equation is based on the viewpoint that a steady-state velocity is determined by a thermally activated deformation process wherein the plasticization of the polymer by the gas reduces the activation energy. At low velocities the process is not diffusion-limited, and therefore the logarithm of the velocity is a linear function of pressure and stress. At higher velocities the logarithm of velocity increases less rapidly with stress and pressure because the penetration of gas into the polymer is decreased by the velocity as it constantly generates a fresh gas-polymer interface. The agreement between the equation and the experimental data is demonstrated.