PARAMETERS CONTROLLING INDENTATION FRACTURE-TOUGHNESS VALUES FOR NA2O-K2O-SIO2 GLASSES

Computational studies were conducted to determine the relationships be tween the chemical and physical properties of Na2O-K2O-SiO2 glasses sy nthesised by wet chemical methods. Calculations of non-bridging oxygen content were undertaken from chemical analysis data previously determ ined by atomic absorption spectrometry (AAS). Dynamic Young's modulus (E) was determined by an ultrasonic method and density by water displa cement. A Tukon hardness tester gave both Vickers and Knoop indentatio ns. Indentation (Vickers) fracture toughness (K-1c) values were obtain ed using Blendell's equation. True hardness (H-o) was determined using Knoop indentation and a technique developed by Li et al. Linear and n on-linear regression analyses between K-1c and H-o, E, non-bridging ox ygen 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 ol del test sepa rated K-1c values determined from Vickers and true hardness. Generalis ed equations were developed leading to the conclusion that K-1c. E, an d H-o were a function of the chemical and physical properties of the g lass compositions studied. Incorporation of H-o in place of Vickers ha rdness into calculations significantly reduced K-1c values by 14-18%. (C) 1996 The Institute of Materials.