Theory of chemically induced kink formation on cracks in silica. I.3-D crack Green's functions

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Abstract
This article is the first of a pair on a theory of chemically assisted fracture. It includes the Green's function analysis for a three-dimensional crack with a kink on it. Equations are developed for the activation energy for the motion and nucleation of such kinks using information to be found in the second article regarding the force laws appropriate for water attack of silica. The most general conclusion is that lattice trapping barriers to crack motion (including chemical effects) are associated with a narrow core region of the crack, which is in turn connected to the nature of the interatomic force laws of the material (including the modifications of these force laws induced by chemical reactions). Further, it is found that the force law must have a severely “snapping” characteristic in order to assure a narrow core, a feature not to be expected except under certain types of external chemical attack of the crack. Additional results are that the energy to nucleate a kink pair in silica under water attack is in the neighborhood of 2 eV and that the motion energy is of order 0.1 eV. Motion energies are expected to be considerably smaller than formation energies in general.

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