Effect of the indenter size on the indentation of aluminum

The indentation behavior of annealed Al was examined using spherical indenters of different radii (0.01, 0.05, 0.1, 0.2 and 0.5 mm). The indentation stress–strain curves displayed similar strain-hardening behavior regardless of the size of indenter, while the altitude increased with the decrease of the size of indenter. A master curve was constructed, which showed different work-hardening behavior from the indentation stress–strain curves. Depending on the size of indenter, the indentation stress–strain curves deviated from the master curve at different levels of stresses. Using the dislocation dynamics, it was found that the initial dislocation density at macroscopic yielding in the indentations was a linear function of the reciprocal of the square root of the size of indenter.