Role of the energy of plastic deformation and the effect of loading rate on nanohardness of soda-lime-silica glass

The role of energy dissipated by plastic deformation during nanohardness testing of a soda-lime-silica glass with a Berkovich indenter for various peak loads (100-1000 mN) as a function of loading rate (1-1000 mN s(-1)) was examined. The maximum increase in nanohardness with loading rate was about 10%. The maximum rate of enhancement in nanohardness with loading rate, was found to occur up to a threshold loading rate (TLR) where a change of deformation mechanism happens. TLR was shown to be linked to the maximum in the relative amount of energy dissipated in plastic deformation which contributed to the enhancement of nanohardness. A new concept of inelastic deformation (IED) parameter was found to describe well the observed trend of nanohardness on loading rate. It was established further that the maximum magnitude of the IED parameter occurred when the relative amount of energy dissipated in plastic deformation during the nanoindentation process was also a maximum. Thus, the interrelation between the amount of energy dissipated in plastic deformation and the IED parameter could be utilized to suggest why the maximum rate of change in enhancement of nanohardness of the present glass with loading rate occurred at the TLR values.