Damage Threshold of Borosilicate Glass Under Plate Impact
Symmetric plate impact tests of borosilicate glass projectiles into borosilicate glass targets were performed at stress levels from 0.7 to 2 GPa (impact velocities from 116 to 351 m/s) As far as the authors know this range of velocities has not been explored in the literature previously. The tests used an ultra high speed camera to record shock and failure propagation. The velocity of the back of the target was also recorded with a photon Doppler velocimeter (PDV) The images clearly show the shock wave and its propagation at the speed expected. The reflected tensile wave is also apparent. What the authors interpret as the failure wave/front is clearly observed and appears at stress levels of 0.8 GPa (velocities as low as 130 m/s) The images apparently show failure nucleation sites that trail the shock wave. These seem to be closer to the shock wave for higher speeds. A possibility is that the defects open faster at higher impact velocity while at lower velocities they are still present but remain undetected. Interestingly, even though the failure wave is clearly seen, the PDV never detected the expected recompression wave. The reason might be that at these low impact velocities the recompression wave is too small to be seen and is lost in the noise. This, in the past, may have confused researchers by thinking that the failure wave was not present at these low impact velocities. This work also presents a new way to interpret the signals from the PDV. By letting part of the signal travel through the target and reflect on the impact side, it is possible to see the PDV signal decrease in intensity with time. This would be consistent with having damage in the interior of the specimen, something not straightforward to confirm through just high speed photography.
Journal of Dynamic Behavior of Materials