The load dependence of the apparent hardness of Si3N4 ceramics is inve
stigated in a wide range of applied loads. It is found that the propor
tional specimen resistance (PSR) model proposed by Li and Bradt is not
suitable for describing the experimental data. A new semi-empirical e
quation is proposed to correlate the indentation size to the applied t
est load. (C) 1998 Elsevier Science B.V.