Analysis of the indentation size effect on the apparent hardness for ceramics

Based on a reasonable assumption that Meyer's law gives an accurate description for the variation of the apparent hardness with indentation size for ceramics, the empirical equation proposed originally by Buckle: P = a(0) + a(1)d + a(2) d(2), is proved sufficiently suitable for representing the original data from the conventional hardness testing. The physical meanings of the parameters included in this equation are discussed in detail. It is shown that the energy-balance relationship can be evaluated completely with this equation, in which the extra energy dissipation and the experimental errors are considered properly. Further analysis reveals that the origin of the indentation size effect on the apparent hardness of ceramics lies in the fact that the traditional definition of hardness, i.e., the ratio of the applied load to the resulting indentation area, is an incomplete description for the energy-balance relationship during indentation. (C) 1999 Elsevier Science B.V. All rights reserved.