Effective cohesive behavior of layers of interatomic planes

A simple model of cleavage in brittle crystals consists of a layer of material containing N atomic planes separating in accordance with an interplanar potential under the action of an opening displacement delta prescribed on the boundary of the layer. The problem addressed in this work concerns the characterization of the constrained minima of the energy E-N of the layer as a function of delta as N becomes large. These minima determine the effective or macroscopic cohesive law of the crystal. The main results presented in this communication are: (i) the computation of the Gamma limit E-0 of E-N as N -> infinity; (ii) the characterization of the minimum values of E-0 as a function of the macroscopic opening displacement; (iii) a proof of uniform convergence of the minima of E-N for the case of nearest-neighbor interactions; and (iv) a proof of uniform convergence of the derivatives of E-N, or tractions, in the same case. The scaling on which the present Gamma-convergence analysis is based has the effect of separating the bulk and surface contributions to the energy. It differs crucially from other scalings employed in the past in that it renders both contributions of the same order.