AFRL Tests Transparent Armor

by Laura Lundin, AFRL Public Affairs
Wright-Patterson Air Force Base

With the goal being to protect military members facing the threat of armor piercing weapons on the battlefield, engineers at the Air Force Research Laboratory are testing a new type of transparent armor, stronger and lighter than traditional materials.

The Air Force Research Laboratory, Materials and Manufacturing Directorate here, in conjunction with the Army Research Laboratory at Aberdeen Proving Grounds, Md., and University of Dayton Research Institute, Ohio, is testing Aluminum Oxynitride (ALONTM) as a replacement for the traditional multi-layered glass transparencies used in existing ground and air armored vehicles.

ALONTM is a ceramic that has high compressive strength and durability and, when polished, is the premier transparent armor for use in armored vehicles, according to 1st Lt. Joseph La Monica, Transparent Armor Sub-Direction lead, for the directorate’s Electronic and Optical Materials Branch. “The substance itself is light years ahead of glass,” said the lieutenant, and offers “higher performance and lighter weight.”

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

ALONTM is virtually scratch resistant, offers substantial impact resistance, and provides better durability and protection against armor piercing threats, at roughly half the weight and half the thickness of traditional glass transparent armor, said the lieutenant.

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

In extensive testing, ALONTM has performed well against multiple hits of .30 caliber armor piercing threats, typical of anti-aircraft fire, and Lieutenant La Monica said tests focusing on multiple hits from .50 caliber threats and Improvised Explosive Devices are in the works.

The lieutenant is optimistic about the results because the physical properties and design of the material are intended to stop higher level threats. “The higher the threat the more savings you’re going to get because with glass, to get the protection against higher threats, you have to keep building layers upon layers of glass, but, with ALONTM, the material only needs to be increased a few millimeters.”

This ability to add the needed protection with only a small amount of material is very advantageous according to Ron Hoffman, an investigator at University of Dayton Research Institute. “When looking at higher level threats, you want the protection, not the weight,” said Mr. Hoffman. “Achieving protection at lighter weights will allow the armor to be more easily integrated into vehicles.”

For example, Mr. Hoffman explained that in order to get the protection against higher level threats with traditional glass, the glass is layered and the weight increases; this weight increase eventually causes problems for vehicles, which, in time, will have to be reconfigured to carry the added weight. “For the more advanced threats that are out there, the increased weight of the armor is getting huge. We eventually have to ask ourselves, how much can the vehicles take?” said Mr. Hoffman.

Mr. Hoffman also pointed out the benefit of durability with ALONTM. “Eventually, with a conventional glass surface, degradation takes place and results in a loss of transparency,” said Hoffman. “Things such as sand have little or no impact on ALONTM, and it probably has a life expectancy many times that of glass.”

This scratch-resistant quality will greatly increase the transparency of the armor, giving military members more visual awareness on the battlefield. “It all comes down to survivability and being able to see what’s out there and to make decisions while having the added protection,” said Mr. Hoffman.

While the Army is looking at using ALONTM Transparent Armor as windows in ground vehicles, such as Humvees, Lieutenant La Monica said the Air Force is exploring its use for “in-flight protective transparencies, for low, slow-flying aircraft, which are any of the C-130 variations, the C-17, the A-10 and any of the helicopters.”

Though the possibilities of this material seem limitless, manufacturability, size and cost are issues the lab is dealing with before ALONTM Transparent Armor can be transitioned to the field, according to the lieutenant. “Traditional transparent armor costs a little over three dollars per square inch; when you look at ALONTM Transparent Armor, the cost is $10 to $15 per square inch,” said Lieutenant La Monica. “The difficulties arise with heating and polishing processes, which, in turn, lead to higher costs, but we are looking at more cost-effective alternatives.”

On a more positive side, Lieutenant La Monica said experimenting with the polishing process has proven beneficial. “We found that by polishing it a certain way, we increased the strength of the material by two-fold,” he said.

As of now, size is also limited because equipment needed to heat larger pieces is expensive. To help lower the costs, the lieutenant said researchers are looking at design variations that use smaller pieces of the armor 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,” he said.

Lieutenant La Monica emphasized that once the material can be manufactured in large quantities to meet the military’s needs, and the cost brought down, the durability and strength of ALONTM will prove beneficial to the warfighter. “It might cost more in the beginning, but it is going to cost less in the long run because you are going to have to replace it less,” he said.

As well as the technological and scientific advances evident with ALONTM Transparent Armor, researchers understand and are motivated by the overall protective benefit to the troops. “This is a good idea for protecting our service members,” the lieutenant said.

October 11, 2005