A different type of indentation size effect

Pop-in during nanoindentation, which indicates the onset of dislocation plasticity, was systematically investigated in annealed and pre-strained single crystals of nickel using spherical indenters with different tip radii. As the indenter radius and pre-strain decrease, the maximum shear stresses determined from the pop-in loads increase. This represents a new type of indentation size effect (ISE), based not on the measured hardness as in conventional ISE, but on the stress needed to initiate dislocation plasticity. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.