Laser‐Shock‐Induced Spall and the Intrinsic Strength of Glass

High strain-rate (~107/s), 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 (1–2 GPa, accounting for wave attenuation) 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 3-mm-thick glass samples. Long-pulse tests (185 ns) with lower peak stresses were decidedly more damaging than those using short pulses (10 ns) but with higher peak stresses, emphasizing the importance of the duration of applied stress in addition to its magnitude. Finally, a surprisingly good correlation in stress–strain relations for fused silica between that obtained via quasi-static techniques and flyer-plate testing likely arises from a lack of irreversible processes and minimal heating during compression up to 9 GPa.