Delayed Crack Growth in Polycarbonate

Abstract

The delayed crack growth rate dc/dt is generally expressed as a function of stress intensity factor K as follows:dc/dt=a1Kmwhere a1 and m are constants that depend on several external factors. From the nucleation theory, Yokobori suggested that these constants were functions of temperature, surface energy, etc. However, there have been few experimental studies about the dependence of these constants upon external factors, although such a study is important to clarify the delayed crack growth mechanism.The present experiment was carried out to investigate the effect of environment on a1 and m by using a high polymeric solid, namely polycarbonate. It is hoped that the results are applicable to the study of metals because of the similarity in delayed crack growth rate between high polymers and metals. The main results obtained are summarized as follows:(1) There are two types of delayed crack growth; one is characteristic of the crack growth in air and another is that in the environment.(2) The environmental delayed crack growth process consists of three stages.(3) At the stage of stable crack growth, the growth rate is expressed as the power function of stress intensity factor. The power varies depending upon the kind of environment.