STRAIN GRADIENT PLASTICITY - THEORY AND EXPERIMENT

Dislocation theory is used to invoke a strain gradient theory of rate independent plasticity. Hardening is assumed to result from the accumu lation of both randomly stored and geometrically necessary dislocation s. The density of the geometrically necessary dislocations scales with the gradient of plastic strain. A deformation theory of plasticity is introduced to represent in a phenomenological manner the relative rol es of strain hardening and strain gradient hardening. The theory is a nonlinear generalization of Cosserat couple stress theory. Tension and torsion experiments on thin copper wires confirm the presence of stra in gradient hardening. The experiments are interpreted in the light of the new theory.