Inert failure strain measurements of sodium borate glass fibres

The two-point bend (TPB) technique was used to measure the failure strains of freshly-drawn xNa2O.(100−x)B2O3 glass fibres under liquid nitrogen. In such experiments, the effects of extrinsic flaws and environmental fatigue are minimised so that intrinsic failure characteristics might be determined and related to glass composition and structure. The inert failure strain for pure B2O3 glass ranges between 29 and 36%; to our knowledge this is the largest inert failure strain ever reported for an oxide glass in a TPB experiment. Failure strains decrease systematically with increasing Na2O content. The addition of Na2O increases the dimensionality and connectivity of the borate glass structure, increasing Young’s elastic modulus and hence increasing resistance to deformation before failure. Similar correlations between inert failure strain and network connectivity have been reported for silicate and aluminosilicate glasses, and may be related to the resistance to crack initiation of the glass network.