Parameters controlling indentation fracture toughness values for Na2O-K2O-SiO2 glasses

Computational studies were conducted to determine the relationships between the chemical and physical properties of Na 2 O-K 2 O-SiO 2 glasses synthesised by wet chemical methods. Calculation of non-bridging oxygen content were undertaken from chemical analysis data previously determined by atomic absorption spectrometry (AAS). Dynamic Young's modulus (E) was determined by an ultrasonic method and density by water displacement. A Tukon hardness tester gave both Vickers and Knoop indentations. Indentation (Vickers) fracture toughness (K 1c ) values were obtained using Blendell's equation. True hardness (H 0 ) was determined using Knoop indentation and a technique developed by Li et al. Linear and non-linear regression analyses between K 1c and H 0 , E, non-bridging oxygen content, and density were significant for all the above variables. The K 1c values using Vickers hardness ranged from 0.98±0.03 to 2.06±0.1 MN/m 3/2 and using true hardness from 0.84±0.05 to 1.68±0.02 MN/m 3/2 . A Student-Newman-Keuls rank order test separated K 1c values determined from Vickers and true hardness. Generalised equations were developed leading to the conclusion that K 1c , E, and H 0 were a function of the chemical and physical properties of the glass compositions studied. Incorporation of H 0 in place of Vickers hardness into calculations significantly reduced K 1c values by 14-18%.