MICROMECHANICAL AND THERMODYNAMICAL ASPECTS OF ENVIRONMENTAL CRAZING [Review]

摘要

The present study aims 1) to investigate theoretically the relation between the craze microstructure and the basic materials parameters such as the yield stress and the surface energy and 2) to provide a detailed thermodynamic treatment of a single isolated craze in glassy polymer tested in an aggressive liquid environment. Based on the assumption that the craze tip is somewhat blunted by small scale yielding and on the Taylor meniscus instability as the mechanism responsible for the propagation of the leading edge of the craze, the detailed micromechanical analysis is used to provide estimates of the critical opening displacement of the craze for growth initiation, mean fibril spacing, mean fibril diameter and fibril volume fraction at the craze tip. The influence of aggressive liquid environments on the yield stress and the surface energy is discussed together with predicted changes in the craze microstructure. The thermodynamic analysis starts with the recognition that induced high negative pressures around the craze tip can increase the solubility of a liquid at this site by several orders of magnitude. As a consequence the local density of thermodynamic potential drops significantly. This unbalanced fall in thermodynamic potential provides an additional driving force for the craze advance. It is shown that a corresponding release of external load is required to preserve the overall balance of the specimen with craze. [References: 36]