High velocity fracture investigation in alumina

Experiments have been performed to investigate the fracture behavior of pressure wave loaded alumina tiles. The waves were produced by impacting steel projectiles at a speed range between 100 and 1200 m/s. The investigation of the damage generation phase was made possible by a newly developed special loading and observation arrangement. The tiles were impacted edge-on and observed was one of the large surfaces by a photographic high-speed technique in combination with the shadow optical method. The aim was to observe the fracture appearance and, based on this, to understand energy absorbing processes. The results are compared with those of earlier experiments with glass slabs. It has been found that alumina behaves quite different than glass. From a fracture mechanic point of view it is most surprising that no distinct terminal crack velocity could be found as is expected and was experienced with glass. Although for certain loading conditions the crack velocity seems to be terminated, different terminal crack velocities are measured for different situations. Two energy absorption mechanisms are discussed