Evaluation of indentation fracture toughness methods for glass biomaterials

Eight formulae from the literature for calculating the indentation fracture toughness K 1c from indendation cracks in the Palmqvist crack regime were evaluated. Values of K 1c ranged from 1.02±0.05 to 1.89±0.03 MN/m 3/2 for an eight component experimental glass, 0.95±0.03 to 1.48±0.15 MN/m 3/2 for a three component experimental glass, 1.60±0.02 to 3.52±0.14 MN/m 3/2 for fused silica, 1.05±0.03 to 1.47±0.03 MN/m 3/2 for soda lime glass, and 1.60±0.02 to 2.31±0.07 MN/m 3/2 for borosilicate glass. Dimensional analysis of relationships for Palmqvist and median cracks showed that the first three equations were in good agreement for the five glasses tested. The five other formulae showed higher values for K 1c and produced different ranking. A Student-Newman-Keuls rank order test did not separate mean values of K 1c for three out of five materials using the first three formulae. For two other glasses no separation occurred for the first two formulae. For the fifth glass no separation occurred for the second and third formulae. All materials evaluated were in the Palmqvist crack regime, in such cases, the three formulae mentioned above are recommended to be used for calculating the indentation fracture toughness K 1c