Abstract
The variation of apparent KIc with crack length is being studied using a variety of commercial ceramic materials. Test methodology is much the same as has been used in the past for natural rock (notched bend test). Where sufficiently definitive data have been obtained, each material showed decreasing KIc with decreasing crack length with all values falling below KIc determined using constant K specimens (double torsion or constant-moment-arm tests). Included in the study was soda-lime glass because it was anticipated that no size effect would occur. Large variations (a factor of two) did occur, however, differing in that all values were above constant K specimen KIc. Post-mortem fracture surface examination revealed problems that can occur where a specimen-wide sharp crack is not achieved before testing.