A PHENOMENOLOGICAL THEORY FOR STRAIN GRADIENT EFFECTS IN PLASTICITY

A STRAIS GKI\MENT THLOKY of plasticity is introduced, based on the notion of statisGcally stored and geometrically ncccsaary dislocations. The strain gradient theory tits within the general framework of couple stress theory and involves a single material length scale 1. Minimum principles are developed for both deformation and flow theory versions of the theory which in the limit of vanishing 1. rcducc to lhcir conventional counterparts: J2 deformation and J, flow theory. The strain gradient theory is used to calculate the size cffcct associated with macroscopic strengthening due to a dilute concentration of bonded rlgid particles: similarly, predictions are given for the effect of void size upon the macroscopic softening due to a dilute concentration of voids. Constitutlvc potentials arc derived for this purpose. I