Theory of chemically induced kink formation on cracks in silica. II. Force law calculations

Abstract

This article is this second of a pair on a theory of chemically assisted fracture. In it a simple bond orbital model of the force laws to be used in fracture is developed. In the bond orbital model, only a few of the atoms in the vicinity of the bond to be broken are considered and do not include interactions with the rest of the system, which is assumed to be Newtonian. Numerical accuracy is not required, but qualitative features of the force laws are believed to be valid. The silica bond is shown to rise quickly to a high peak, after which it develops a relatively long tail. When the bond is attacked by water, modeling by the same technique indicates that the bond has a “snapping” characteristic that is important in the theory developed in the first article. For bonds with smooth “back sides” the barriers to crack motion are shown to be low, but barriers are expected to be observable when the bond snaps. A tight binding treatment of a one-dimensional chain has been included in order to investigate the effect of including band effects in the force law. These effects are found to be small compared to the simple bond breaking of the bond orbital calculation.