A chemical dissolution technique for challenging existing constitutive   models of the densification process beneath an indentation imprint in   amorphous silica
  The region of permanent densification beneath a Berkovich indentation imprint in silica glass is investigated using a novel chemical dissolution technique. The use of the similitude regime in sharp indentation testing allows one to record reliable data with a good spatial resolution that makes it possible to deal with low loads (typically below 10 mN) and crack-free imprints. The densified zone dissolves much quicker than the non densified regions. The analysis of the results, along the vertical axis, indicates that the densification zone is rather homogeneous with a steep transition to the non densified zone. The size of the densification zone, with respect to the initial free surface, is estimated to be around 1.9 the maximum penetration depth of the instrumented indentation test. These findings are compared with former experimental data and critically compared with the results of numerical simulations from selected constitutive equations and other numerical techniques from the literature. These comparisons highlight some advantages and disadvantages of existing modelings and thus call for further advanced progress on that matter. They nevertheless favor mostly the contribution of the densification process with respect to the plastic flow (volume conservative process) in creating a permanent imprint. 
J.-P. Guin, V. Keryvin, L. Charleux, K. Han, J.-C. Sangleboeuf, M.   Ferry
cond-mat.mtrl-sci