Analysis of the Fragmentation of AlON and Spinel Under Ballistic Impact

Abstract

It has been demonstrated that significant weight reductions can be achieved, compared to conventional glass-based armor, when a transparent ceramic is used as the strike face on a glass-polymer laminate. Magnesium aluminate spinel (MgAl 2 O 4 ) and AlON are promising candidate materials for application as a hard front layer in transparent armor. Comprehensive, systematic investigations of the fragmentation of ceramics have shown that the mode of fragmentation is one of the key parameters influencing the ballistic resistance of ceramics. In the study described here, the fragmentation of AlON and three types of spinel was analyzed: two types of fine grained spinel with nominal average grain sizes 0.6 lm and 1.6 lm and a bimodal grain-sized spinel with large grains of 250 lm size in a fine grain (5-20 lm) matrix were examined. The ceramic specimens of 6-mm thickness were glued to an aluminum backing and impacted with armor piercing (AP) projectiles of caliber 7.62 mm at two different velocities-850 m/s and 1100 m/s. The targets were integrated into a target box, which allowed for an almost complete recovery and analysis of the ceramic fragments. Different types of high-speed cameras were applied in order to visualize the different phases of fragment formation and ejection. A laser light-sheet illumination technique was applied in combination with high-speed cameras in order to determine size and speed of ejected ceramic fragments during projectile penetration. The application of the visualization techniques allowed for the analysis of the dynamics of the fragment formation and interaction with the projectile. A significant difference in the fragment size distributions of bimodal grain-sized spinel and AlON was observed.

Transparent Ceramics at 50: Progress Made and Further Prospects

“…Numerous investigations resulted in a similar ballistic performance of transparent AlON and spinel armor tiles, depending on the testing procedure and on the tested grades of these ceramics sometimes with some advantage of the ballistic strength of spinel or of AlON …”

Novel Methods in Terminal Ballistics and Mechanochemistry of Damage: A Review of Developments at the US Army Research Laboratory, 2001-2007

“…Fortunately, I eventually discovered various photographs of bullets penetrating brittle plates similar to the illustration in Fig. 1, which shows the loss of axial symmetry by means of the appearance of radial cracks caused by the bullet penetrating through transparent armor (see many wonderful photographs in Strassburger et al 15 ).…”

An Introduction to the Properties of Silica Glass in Ballistic Applications

“…The only alternative for armoured windows at the moment is fine‐grained polycrystalline AlON . Silica glass, however, is intrinsically transparent due to its amorphous structure and appropriate band gap .…”