stronger.” Through use of geometrically self-similar indenters such as cones and pyramids,
the size effect is manifested as an increase in hardness with decreasing depth of penetration
and becomes important at depths of less than approximately 1 μm. For spherical indenters,
the diameter of the sphere is the most important length scale; spheres with diameters of less
than approximately 100 μm produce measurably higher hardnesses. We critically review …