Computational approach to phenomenological mesoscopic field dislocation mechanics.

摘要

A variety of physically observed size-effects and patterning behavior in plastic response at the micron scale and below have raised interesting challenges for the modeling of plastic flow at these scales. In this thesis, two such models appropriate for length scales of 0.1mum and 0.1mum-100mum are considered. The first (FDM) is conceptually appropriate for scales where all dislocations are resolved. The second (PMFDM) is a moving space-time averaged version of the first, appropriate for mesoscopic plasticity.; In the first part of the thesis, FDM is shown to be capable of representing the elastic stress fields of dislocation distributions in a generally anisotropic medium of finite extent. It is also shown to have some success, naturally limited as expected, in prediction of yield drop, back stress and development of inhomogeneity from homogeneous initial conditions and boundary conditions which would otherwise produce homogeneous deformation in conventional plasticity.; The space-time averaged version of FDM, PMFDM, requires additional closure statements due to the inherent nonlinearity of FDM. This is achieved through the use of a robust macroscopic model of strain-gradient plasticity that attempts to model effects of geometrically-necessary dislocations only in work-hardening. Finite element method-based computational predictions of the theory demonstrate several experimentally observed features of meso and macro scale plasticity. The model, which fundamentally accounts for fine scale dislocation mechanisms, seems to be an adequate representation of plasticity for these scales.