Discrete Crystal Plasticity

This article is concerned with the development of a discrete theory of crystal elasticity and dislocations in crystals. The theory is founded upon suitable adaptations to crystal lattices of elements of algebraic topology and differential calculus such as chain complexes and homology groups, differential forms and operators, and a theory of integration of forms. In particular, we define the lattice complex of a number of commonly encountered lattices, including body-centered cubic and face-centered cubic lattices. We show that material frame indifference naturally leads to discrete notions of stress and strain in lattices. Lattice defects such as dislocations are introduced by means of locally lattice-invariant–but globally incompatible–eigendeformations. The geometrical framework affords discrete analogs of fundamental objects and relations of the theory of linear elastic dislocations, such as the dislocation density tensor, the equation of conservation of Burgers vector, Kröner’s relation and Mura’s formula for the stored energy. We additionally supply conditions for the existence of equilibrium displacement and slip fields; we show that linear elasticity is recovered as the Γ -limit of harmonic lattice statics as the lattice parameter becomes vanishingly small; and we compute the Γ -limit of dilute dislocation ensembles. In this latter case, the Γ -limit of the stored energy function supplies a generalization of the prelogarithmic energy factor of the theory of linear-elastic dislocations. 2 M. P. ARIZA AND M. ORTIZ