Microhardness indentation application and limitation in fracture-toughness evaluation of ceramics

The use of a microhardness indentation as a controlled flaw in a flexural specimen for measuring fracture toughness in advanced ceramics is critically evaluated. From a review of fracture-toughness testing methodologies for ceramics, it is shown that currently there are not any standardized or widely agreed upon K sub Ic test procedures. The problems associated with the controlled flaw test are discussed and analyzed. An experimental program is used to investigate the effects of residual stress on the measurement of fracture toughness in a wide variety of sintered and hot-pressed advanced ceramics, including TiB sub 2 , Al sub 2 O sub 3 , SiC, ZrO sub 2 , Si sub 3 N sub 4 . The validity of the test procedure for evaluating K sub Ic of advanced ceramics in general is put forth.