Abstract: The theories on nanoindentation are presented and the shortcomings of each one are pointed out. On the basis of experiments and the fact that the indenting load F can be expressed as a quadratic polynomial, a new definition of microhardness is given. By dimension analysis we can see that microhardness consists of two parts, the first one is a constant and independent of the indented depth. The second one is dependent of the indented depth and increases dramatically as the depth gets small.

Key words: Contact mechanics, Elastic modulus, Microhardness, Nanoindentation, Strain gradient