Network and void structures for glasses with a higher resistance to crack formation

To clarify the nanoscale deformation and fracture behaviors of glass under stress, changes in the network and void structures of xNa2O–(1 − x)SiO2 glasses are investigated at a constant strain rate via molecular dynamics (MD) simulation and volume rendering methods. Glasses with higher Na2O contents have lower polymerized network structures and lower Youngʹs moduli, but exhibit smaller total void volumes and void sizes. Under tension, network breakdown increases the total void volume and void size of SiO2 glass. Hence, SiO2 glass breaks at a relatively small strain due to decreased flow. In contrast, network rearrangement slightly increases the void volume and void size of Na2O-containing glass. Consequently, Na2O-containing glass breaks at a larger strain due to increased flow. Under compression, SiO2 glass shows a larger densification than Na2O-containing glasses, because densification is attributed to crushing larger voids into smaller voids. These results indicate that controlling the structure is crucial to suppress crack formation because the network and void structures strongly affect deformation and fracture.