On the current understanding of strain gradient plasticity

Some current strain gradient plasticity theories of non-homogeneous deformation and size effects are discussed critically, in particular with respect to the question how the density of geometrically necessary dislocations contributes to the flow stress. In an increasing number of recent strain gradient plasticity theories, the microscopic dislocation processes are not taken adequately into account, and the physical meaning of the internal material length scales involved remains vague. The need for more microstructurally based physical models and critical experiments is emphasized.