High strain-rate spall threshold results obtained via laser-shock testing are reported for three glasses (fused silica, soda-lime "float" glass, and a borosilicate); such tests should be immune to the influence of surface flaws as the plane of failure is not localized at a surface. Whereas the measured spall thresholds agree reasonably well with conventional, flyer-plate shock-wave experiments, they are 5-10 times lower than "intrinsic" strength values obtained from quasi-static tests. This is speculated due to the rapid compress/decompress loading cycle arising from free-surface reflection. Attenuation effects associated with the ramp wave inherent to glasses of this study was the likely basis for the difference in spall threshold between 2- and 3mm-thick glass samples.
