Transparent armour

Engineers at the US Air Force Research Laboratory are testing a new type of transparent armour that is stronger and lighter than traditional materials.

The Air Force Research Laboratory, Materials and Manufacturing Directorate in conjunction with the Army Research Laboratory at Aberdeen Proving Grounds, MD, and University of Dayton Research Institute, OH is testing Aluminium Oxynitride , or ALON, as a replacement for the traditional multi-layered glass transparencies used in existing ground and air armoured vehicles.

Traditional transparent armour is created by bonding thick layers of glass together. ALON Transparent Armour is created by combining the transparent ALON piece as a strike plate, a middle section of glass and a polymer backing, each visibly thinner than the traditional layers.

The ALON material is virtually scratch resistant, offers substantial impact resistance, and provides better durability and protection against armour piercing threats, at roughly half the weight and half the thickness of traditional glass transparent armour.

In a demonstration at FortDrum’s Team Patriot East in June 2004, ALON test pieces held up to both a .30 calibre Russian M-44 sniper rifle and a .50 calibre Browning Sniper Rifle with armour piercing bullets. While the bullets pierced the glass samples, the ALON withstood the impact, resulting in no penetration.

While the US Army is looking at using ALON transparent armour as windows in ground vehicles, such as Humvees, the Air Force is exploring its use in slow-flying aircraft, such as the C-130 Hercules and the C-17 Globemaster III.

Though the possibilities of the material seem limitless, manufacturability, size and cost are issues the lab is dealing with before ALON Transparent Armour can used in the field. Traditional transparent armour costs a little over three dollars per square inch, but ALON Transparent Armour costs $10 to $15 per square inch because of the heating and polishing processes involved in its manufacture.

On a more positive note, experimenting with the polishing process has proven beneficial. Polishing the material in a certain way can increase the strength of the material by two-fold.

Today, size is also limited because equipment needed to heat larger pieces is expensive. To help lower the costs, researchers are looking at design variations that use smaller pieces of the armour tiled together to form larger windows. Lowering cost by using a commercial grade material is also an option, and the results have been promising. So far, the difference between the lower grade material and higher purity in ballistic tests is minimal.