Method to account for true contact area in soda-lime glass during nanoindentation with the Berkovich tip

An empirical relationship for estimating the pile-up contact area from the contact stiffness, S and the contact depth, hc, has been developed. This was achieved first by using the atomic force microscope to image nanoindents made with the Berkovich indenter in soda-lime glass and approximating the pile-up contact perimeter as a semi-ellipse. Then, by determining the pile-up contact area for several peak indentation loads, a correlation was found between the pile-up contact area and the load used to generate it. The importance of this new method of determining the pile-up contact area is that the need for indent imaging is made completely redundant, since the contact stiffness is a quantity that is routinely obtained during nanoindentation data analysis. Elastic modulus of soda-lime glass of 70 ± 1.5 GPa is measured with loads ranging from 20 to 500 mN. The hardness measured also falls within the range of values, 5.2–5.9 GPa, normally quoted in the literature for the glass.