Abstract
Mechanical behavior and structure of glass under pressure and stress were investigated to seek a guiding principle for obtaining a less brittle glass. A new simple method for measurement of brittleness was proposed by using the concept of brittleness defined from deformation and fracture behaviors. Using this method, brittleness was measured for various kinds of glasses. It was found that in the case of normal glasses, the brittleness decreased monotonically with decreasing density, while in the case of anomalous glasses, the brittleness increased with decreasing density. As a result, in most silicate glass systems, a minimum brittleness appeared at a certain density in the transition region from normal glass to anomalous glass. The glasses in the minimum region showed easier deformation and higher cracking-resistance. A 50% decrease in brittleness resulted in the increase of crack initiation load by about 15 times. To clarify structural change during deformation and fracture, molecular dynamics simulation was carried out for glasses with different brittleness. When the glasses were subjected to relatively low pressure and stress, they showed mostly elastic deformation caused by changing bond angle of Si-O-Si. With increasing pressure and stress, they showed inelastic deformation due to flow and densification besides elastic deformation. The inelastic deformation resulted from the movement of modifier ions and the rearrangement of network structure. Finally, the glasses fractured, forming cavities in the network. It was concluded that a higher polymerized network and an easier movement of modifier ions were important for lower brittleness, which can be related to easier deformation and more difficult cavitation, namely, more difficult cracking.
