Accurate evaluation of critical flaw size in structural ceramics via femtosecond laser

Critical flaw size of structural ceramics is generally less than 100 μm and is therefore too small to be reliably evaluated. In this study, micro-sized flaws (as small as 10 µm) were introduced via femtosecond laser for the first time, and the critical flaw sizes of ZrB₂ and ZrB₂-SiC-Graphite ceramics (12.9 µm and 36.1 µm, respectively) were accurately evaluated by linear extrapolation in double logarithmic coordinates. The critical flaw sizes calculated from the indentation fracture toughness (14.3 µm and 34.3 µm for ZrB₂ and ZrB₂-SiC-Graphite ceramics, respectively) agreed well with the experimental results, while significant overestimation would occur by using fracture toughness values measured by means of single-edge notched beam, single-edge V-notched beam and single-edge precracked beam methods, which was mainly due to the fact that the notches in these three tests had the depth scale nearly two orders of magnitude higher than those of the inherent flaws.