Photon Doppler Velocimetry Measurements of Impact-Induced Surface Waves in Glass and Their Role in Fracture Initiation and Damage Evolution

Ballistic experiments involving the impact of cylindrical Lexan (R) projectiles, with nominal velocities of 400 and 800 m/s, on borosilicate glass targets were conducted using a single-stage gas gun. The objective of the experiments was to develop a technique involving multiplexed photon Doppler velocimetry (PDV) to observe the distal surface motion due to the propagation of impact-induced elastic waves. Comparison of the recorded signals to finite-element simulations of the experiment allowed for the identification of the signature of fracture initiation and subsequent damage evolution in the material. By directing PDV probes through the rear surface of the target it was also found that the surface motion within the impact zone could be measured. In addition, it was discovered that two distinct velocity signals could be consistently measured beneath the impact site. One of these signals was identified as the particle velocity of the impact surface. The other signal is presently of unknown origin.