Molecular dynamics study of acoustic velocity in silicate glass under irradiation

The development of a molecular dynamics method simulating the propagation of acoustic waves allowed their propagation velocities to be measured in borosilicate glasses. The qualitative results obtained in glass irradiated by heavy ions correctly reproduces the experimental results, i.e. a reduction in the acoustic wave propagation velocity in irradiated glass. These changes in the mechanical properties were correlated with structural changes, in particular increased disorder in the glass. The greater disorder results in broadening of the characteristic distributions of the glass: distances, angles, and ring sizes. Similarities were clearly observed between the effects of irradiation and the effects of higher quenching rates on the acoustic wave propagation velocities. An additional study of glass artificially expanded by homothetic volume transformation shows that a reduction in acoustic velocity is not necessarily associated with swelling. The artificial volume change combined with increased stresses in the glass results in higher acoustic velocities.