Army engineers are developing a new color-changing paint formula that will tell soldiers if their ammunition is safe to use just by looking at the color.
Known as Thermal Indicating Paint, the formula uses thermochromic polymers to detect temperature ranges that ammunition was exposed to during transport and storage. Researchers foresee non-military applications as well, perhaps in assisting first responders in emergency situations.
Thermal Indicating Paints, in development since 2008, are among many "smart" coatings being developed at the Picatinny Arsenal, in New Jersey. Researchers believe the coatings can not only improve ammunition performance, but may save soldiers’ lives.
Thermal indicating paints
can detect a range of
temperature bands and
display a distinct color
for each range.
Storing ammunition at high temperatures can comprise its integrity and performance. When propelling charges are exposed to high temperatures for extended periods, the propellant stabilizer can rapidly deplete, creating the potential for auto-ignition. In addition, firing overheated propellant can lead to dangerous, elevated gun pressures that cause weapon failure and injure the soldier.
There have been documented incidents of failures caused by thermal exposures during Operation Desert Storm and recent conflicts in Iraq and Afghanistan, reports the Army’s Armament Research, Development and Engineering Center (ARDEC), which is testing the paint formulations at Picatinny.
Picatinny is an armament R&D center that provides virtually all of the lethal mechanisms used in Army weapon systems and those of the other military services. The New Jersey Institute of Technology is also partnering on the paint project.
Beyond Mood Rings
Thermal Indicating Paints draw on the same technology as mood rings—thermochromic objects that change color in response to the wearer’s body temperature. The thermochromic element changes the light wavelength when exposed to different temperatures.
The Army’s Armament Research, Development
and Engineering Center is using equipment
at Picatinny Arsenal to test the paint
With paint, however, the challenge is making the color change permanent.
"We have formulas that change color within the designated temperature ranges, but our biggest challenge is maintaining long-term stability of a coating," said James Zunino, Project Officer / Materials Engineer, ARDEC.
"We have to develop a paint that will survive in military operating conditions, including harsh temperatures and wind blasts."
Ammunition is often exposed to extreme temperatures throughout combat operations—from transport and storage to pre-positioning. Middle East combat temperatures inside munitions containers can exceed 190 degrees Fahrenheit, Picatinny officials say. (Water boils at 212 degrees Fahrenheit.)
"Thermal Indicating Paints can help prevent warfighters from using ammo that may have been compromised by exposure to environmental conditions outside of design limits," Zunino said. "It could reduce the amount of accidents that could happen, it can reduce the logistical burden of transporting and storing munitions, and it gives increased survivability to the soldier."
Paint would also cost only pennies per application, compared to costly temperature gauges the Army now uses on its larger caliber ammunition stocks, officials say.
High Explosives Tested First
The team is developing cost-effective and commercially available formulations that can detect four heat ranges (in degrees Fahrenheit): 145-164, 165-184, 185-200, and above 200. The 30mm High Explosive (HE) round is set to be tested first.
"We're starting with the 30mm family of ammo, because they aren't expensive enough rounds to deem the use of a costly temperature gauge or monitor,” said Zunino. “The savings are bigger, because it's low-value, high-volume assets."
The team plans to have a formula ready for trial testing within the year, Zunino said.
‘Very Inexpensive Telltale’
"The desired outcome in the Class V (ammo) world would be a very inexpensive telltale that soldiers and logisticians could use to identify munitions that had experienced temperature exposures outside design limits," said Mitch Hillard, Program Specialist, Project Director Joint Services (AMMOLOG), which is managing the program.
"Such munitions could then be set aside for test and analysis to provide feedback to the development community on the performance and safety effects of extreme environmental exposures."
‘Smart’ Coating Progress
Researchers have reported considerable progress in the coatings in the last year. They say they have expanded the paints’ temperature ranges and added the capability to detect how long the munition was exposed to high temperatures.
The length of exposure is determined with a hand-held laser system, which causes changes in the coating’s optical reflectivity.