Material-length-scale-controlled nanoindentation size effects due to strain-gradient plasticity Original Research Article

This paper proposes a concept of strain-gradient plasticity that is based on characteristic material length scale. Experimental results for indentation size effect are correlated with the predictions from a dislocation-based strain-gradient plasticity model. Nanoindentations on single crystals of Al, Ag, Ni, polycrystalline Cu and poly-synthetically twinned (PST) lamellar α2- and γ-TiAl are conducted with an atomic force microscope with an add-on force transducer from Hysitron, Inc. It is found that the indentation size effect is controlled by a characteristic material length scale l, which is a function of the Burger’s vector, the shear modulus, and a material reference stress. The material length scales are found to be in the order lAg>lNi>lAl>lCu>lα2-TiAl>lγ-TiAl, which corresponds to the indentation size effect.