Improved Modelling of Bauschinger Effects in Plastic Flow

Existing, continuum-based models of plasticity cannot account for the Baushcinger effect and other asymmetries in plastic flow. This is because the Bauschinger effect has its origin in atomic-scale lattice defects known as dislocations. Dislocation propagation causes local shears, subject to rigid selection rules, which are not part of the continuum framework. Specifically, when obstacles to plastic flow are present, such as non-deformable dispersoids, the local dislocation density increases with deformation to satisfy compatibility conditions. On refersal of the applied stress, this excess dislocation content collapses and leads to a reduced flow stress, the classical Bauschinger effect. There are other asymmetries in plastic flow which are similarly not part of the continuum picture. The logical approach to this problem is to develop a model in terms of the fundamental defect, the dislocation. The proposed research will be aimed at a fully interacting many-dislocation numerical model, incorporating all of the lattice-based properties of dislocations. In Phase I, the model will be fully defined, and limited computer codes to demonstrate the feasibility of the project will be constructed. Particular attention will be devoted to high strain rate and low temperature conditions, and to interfacing to standard continuum methods.