Spalling in sapphire in different crystallographic directions under shock compression

The tensile strength of single-crystal sapphire specimens with $c$, $a$, $d$, $r$, $n$, $s$, $g$, and m crystallographic orientations ($c$-, $a$-, $d$-, $r$-, $n$-, $s$-, $g$-, and $m$-axis specimens) has been measured under shock compression in the stress range of 15 – 20 GPa. It has been found that the spall strength depends on shock direction and maximum compression strength. The spall strength is greatest, $\sim$ 12 – 13 GPa, in $m$- and $a$-axis sapphire specimens when the maximum shock stress equals 16 GPa.