A reinvestigation of the validity of the indentation fracture (IF) method as applied to ceramics

Poor correlation between indentation fracture resistance, KIFR, and fracture toughness, KIC, has long been considered a weak point of the indentation fracture (IF) method of materials analysis. The present work therefore assessed the reliability of the experimental data that has historically been used for comparisons of KIFR and KIC. A painstaking survey of primary literature reports concerning the IF method revealed that the comparisons of KIC with KIFR in most studies were imperfect because both KIC and KIFR were measured using unreliable techniques and because improper test materials such as silicate glass were employed. These findings indicate that the standard objections against the use of the IF model are not well supported, and also that the majority of the empirically-derived calibration constants used in various IF equations are suspect. Accordingly, it is evident that new experimental measurements using the latest and most reliable techniques will be required to allow well-informed discussions of the validity of this test method in future.