Effect of Crystalline Anisotropy on Shock Propagation in Sapphire (Al2O3)
Abstract
The main goal was to find a transparent material stronger than B4C and SiC that remains transparent under shock compression. Sapphire (Al2O3) was chosen because of its high strength and the large body of experimental data that exists to design experiments and interpret results. Published optical images of sapphire under shock indicate heterogeneous yielding and optical emission, which are probably the cause of shock-induced opacity. Heterogeneous deformation is largest for shocks traveling in the c and a directions of the hexagonal lattice; heterogeneous deformation is lower for shocks traveling in the r direction. We used c-cut, r-cut, and m-cut (basal plane) crystals for a systematic study of the mechanism that causes opacity. Shock experiments on these orientations are being performed by Gennady Kanel under a companion grant. His preliminary results suggest microstructural deformations in c-cut crystals do not occur to the same degree in r-cut. Because the least deformation appears to occur in the orientation with the lowest sound speed, we also obtained crystals with seven orientations to identify the direction with lowest sound speed, the optimal direction. These were sent to ARL for sound speed measurements. Orientations with the lowest sound speeds should be studied in future experiments.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 26, 2007
- Accession Number
- ADA483437
Entities
People
- I. F. Silvera
- W. J. Nellis
Organizations
- Harvard University