Confined Alumina Bar-on-Bar Impact Experiments

In an earlier study on unconfined alumina bar-on-bar impact measured velocity history (using VISAR) data at an impact velocity of 100 m/s showed that the material response is elastic. At higher impact velocities of 220 m/s and 300 m/s, the data suggested the material behavior is inelastic. This study is extended to confined alumina bars. Alumina bars (12.7-mm diameter) were shrunk fit into 3.17 mm thick steel sleeves to provide confinement stress. Axial velocity histories at the far end of the confined AD998 target bar are measured at nominal impact speeds of 200 m/s, 300 m/s, and 500 m/s. Lateral expansion of the confinement sleeve around the impactor and target bars during impact is photographed using a high-speed (Imacon) camera. Peak axial velocities increase from 0.135 mm/μs for unconfined bars to 0.170 mm/μs for confined bars at a nominal impact velocity of 200 m/s. At an impact velocity of ∼300 m/s peak axial velocity of confined bar increase to 0.200 mm/μs from 0.170 mm/μs for unconfined bar. At ∼500 m/s the confinement shatters on impact and peak axial velocity is measured to be almost same as that for ∼200 m/s. These results show that the confinement provided by a 3.17-mm thick steel sleeve to alumina bar enhances its impact response for impact velocities to ∼300 m/s and confined alumina behaves as inelastic at the lowest impact velocity of 200 m/s