GLASS HARDNESS AND ELASTIC MODULUS DETERMINATION BY NANOINDENTATION USING DISPLACEMENT AND ENERGY METHODS

The hardness and elastic modulus of two glasses (soda lime glass and borosilicate glass) were determined by nanoindentation using Oliver and Pharr displacement analysis (O&P method) and two methods based on the energy of deformation developed by Cheng and Cheng (C&C) and Chen and Bull (C&B). Multiloading indentations with peak loads varying between 5 mN and 500 mN were carried out using a Berkovich indenter. The implemented calibrations in O&P analysis taking into account the thermal drift, initial depth, instrument compliance and indenter geometry sources of error, revealed their relative importance on the indentation hardness and reduced modulus. The errors induced by the estimated initial depths and the thermal drift were limited compared to those caused by the instrument compliance and the indenter geometry. The implementation of the instrument compliance was verified by linear regression of the measured compliance variation and by examining the constancy of the ratio of the peak load over the contact stiffness squared at large depths. The calibrated surface area had an important influence on indentation hardness at small depths. The use of the linear C&C method showed that there is no unique value for the indenter constant lambda appropriate for both glasses. Comparison between the two energy methods showed that the results obtained by the linear C&C method with a constant lambda = 5.3 were closer to those obtained by the non linear energy C&B method. The soda lime glass hardness and elastic modulus obtained by these two methods were closer to the values obtained by conventional means. The borosilicate glass conventional values were closer to those obtained by the O&P method.