Classical elasticity has no length scale. Stress concentration factors for holes, cavities, or notches in a classical elastic solid are predicted to be independent of the size of the hole, cavity or notch.
Stress concentration factors for holes are smaller in a Cosserat solid than in a classical solid, via theory. If the hole is sufficiently large, the stress concentration factor is classical but if the hole is small, the stress concentration factor is reduced compared with classical predictions.
R. D. Mindlin, Effect of couple stresses on stress concentrations, Experimental Mechanics, 3, 1-7, (1963).
Stress concentration factors for spherical cavities can be higher in the presence of micromorphic (microstructure elastic) behavior over a range of parameters, via theory.
J. L. Bleustein, Effects of microstructure on the stress concentration at a spherical cavity, Int. J. Solids Structures, 83-104 (1966)
R. D. Mindlin, Micro - structure in linear elasticity, Archive for Rational Mechanics and Analysis 16 51-78 (1964).
In a special type of micromorphic solid, allowing only micro-dilatations but no micro -rotations, the predicted stress concentration factor for a hole is greater than the classical prediction. This is called void elasticity.
S. C. Cowin, The stresses around a hole in a linear elastic material with voids, Q. J. Mech. Appl. Math. 37 , 441-465 (1984)
Void elasticity also predicts size effects in bending but no size effects in torsion.