Visualization and analysis of impact damage in sapphire

This paper reviews work carried out with the fully instrumented Edge-on Impact (EOI) facility at the Ernst-Mach-Institute (EMI), using a Cranz-Schardin high speed camera, modified for dynamic photoelasticity, to quantify stress wave propagation, damage nucleation and propagation during high velocity impacts. The experimental technique has been used to examine monolithic single crystal sapphire plates (100 mm x 100 mm x 10 mm) in crystallographically controlled directions impacted at about 400 m/s with both steel solid cylinders and spheres. The plates were impacted as follows: 100 mm x 100 mm large surface r-plane parallel to the a-axis; large surface a-plane parallel and perpendicular to the c-axis; large surface c-plane parallel to a-axis; and impacting perpendicular to r-plane small surface. In certain orientations damage propagation is clearly by macro-cleavage with significant cleavage branching. The velocities of damage and cleavage propagation are presented.