High-speed photographic study of wave propagation and impact damage in transparent aluminum oxynitride (AlON)

Fused silica and AlON specimens were tested by means of a modified edge-on impact technique. The specimens were placed between crossed polarizers, and the photo-elastic effect was utilized to visualize the stress waves. Pairs of impact tests at approximately equivalent velocities were carried out in transmitted plane shadowgraphs, visualization of damage and crossed polarized light visualization of wave propagation. The experiments provided direct evidence of ceramic damage by nucleation and growth of fracture initiated by the stress waves, ahead of the coherent fracture front growing from the impacted edge. A comparison of the results in a reflected light set-up and the shadowgraphs indicated fracture nucleation in the interior of the ceramic. The experimental results provide a data basis for a deeper analysis of the damage mechanisms by means of numerical simulation. The work was supported by Dr. Douglas Templeton, U.S. Army Tank-Automotive Research, Development and Engineering Center, Warren, MI.