Strain gradient interpretation of size effects

It is shown that the phenomenon of strength dependence on size, for otherwise geometrically similar specimens, may be interpreted on the basis of gradient elasticity and gradient plasticity arguments. This is illustrated by adopting a simple strength of materials approach for considering torsion and bending of solid bars and subsequent comparison with available experimental data. Solutions of boundary value problems based on gradient elasticity and gradient plasticity including those of fracture and shear banding can also be used to interpret size effects in more complex situations. This is not discussed here, however, in order to maintain simplicity and clarity when illustrating the theoretical predictions in comparison with the experimental trends.