The shear strength of a shocked borosilicate glass with an internal interface

Abstract

The shock properties of amorphous silicate glasses, under conditions of one-dimensional strain, have been of interest for a number of years. In the past decade, attention has focused on the shock-induced fracture of these materials, in particular the failure wave. This was first observed by Razorenov et al., from rear surface velocity traces in K19 glass (similar to soda-lime). They noticed a small increase in velocity superimposed on these traces, and interpreted it as the result of the release from the rear surface of the target being partially reflected by a moving front (the failure wave) within the material. As this reflection was recorded as a reload, they concluded that the material behind this front must have undergone a reduction in shock impedance. This led them to suggest that the material had fractured. Several years earlier, Nikolaevski had proposed just such a mechanism for the dynamic failure of brittle solids. Brar et al. also observed this front, using spall strength and lateral stress measurements. Spall strengths were seen to be high ahead of this front, but diminished to zero behind it. They also observed an increase in lateral stress, sometime after the arrival of the main shock. Since the shearmore » strength ({tau}) of any material under one-dimensional shock loading, is expressed as, 2{tau} = {sigma}{sub x} {minus} {sigma}{sub y}, where {sigma}{sub x} and {sigma}{sub y} are the longitudinal and lateral components of stress respectively, it was clear that the material was undergoing a significant reduction in shear strength behind the failure wave. Bourne et al. were also able to observe this moving front in both soda-lime and borosilicate glasses as a loss of opacity, using high-speed photography.« less