DOE OSTI2013
Several siliceous (i.e., materials containing, resembling, relating to or consisting of silica or silicon dioxide) materials were examined in this study conducted by Oak Ridge National Laboratory and sponsored by the US Army TARDEC. Some were glasses (fused silica or fused quartz, Starphire soda lime silicate glass, hydrated Starphire, BOROFLOAT borosilicate glass, an iron-containing soda lime silicate glass, opal (a hydrated silicate glass), ROBAX glass ceramic, and others were single crystal (α-quartz) and polycrystalline (Coesite - a high pressure phase of crystalline quartz) ceramics. Some of these materials are presently used in transparent armor systems or are under consideration for such. The testing of these materials allowed for comparisons of glass types, glass versus glass ceramics, effect of water content, and comparison of amorphous versus crystalline materials of the same composition. The responses of these materials to high pressure loading were studied using spherical indentation testing, diamond anvil cell testing, and laser shock testing. So besides the focus of this study being on the siliceous materials, as much emphasis was placed on the efficacy of these three test methods to exploit high pressure responses. Each test is different and enables the study of different aspects of high pressure response as highlighted below. 1. Spherical indentation, when using small indenter diameters, produces both high pressure and shear, and the loading and unloading histories enabled quantification of apparent yield stress and semi-quantification of energy absorption capability (hysteresis) of the various siliceous materials. 2. Diamond anvil cell testing produces a hydrostatic stress, and when concurrently used with Raman Spectroscopy, enabled the potential identification of changes of state of material as a function of quantified pressure for the various siliceous materials. Permanent densification was also detectable. 3. Laser shock testing produces high pressures but under dynamic conditions (impact event less than 30 ns), so this enabled the study of the effect of rate on high pressure. A previously unobserved damage mechanism was revealed with this testing, and the ease or difficulty of laser-shock-induced damage initiation was deemed to be relatable to the native surface flaw population that exists on these materials.