A fenced-in enclosure looms atop a tall breakwater on the Atlantic Coast of Central America.
Profoundly rusty razor wire coils around the circumference of the fencing, sagging in places. The fence's lone gate is fastened with a massive padlock that takes patient working to unfasten. Both the razor wire and the lock are less than six months old.
Welcome to the U.S. Army Tropic Regions Test Center (TRTC) breakwater exposure site.
"The breakwater environment is quite aggressive," said Luisa Wong, test officer. "Corrosion occurs twice as fast here as the normal coastal environment."
In fact, this particular location has been characterized as one of the most saline-saturated in the world, yet one of the test center's relatively benign coastal sites is only several football field-lengths away.
Such is a small portion of the world of microclimates in which TRTC characterizes and tests all manner of equipment. The customers for exposure testing range from the branches of the United States military and those of friendly foreign nations, to private industry, and academia. TRTC testers expose all manner of equipment in tropical environments, from small samples of paint and metal to uniforms, rucksacks, and weapons.
"Corrosion is logarithmic," said Ernest Hugh, TRTC director. "It starts quickly, then levels off."
At the breakwater site, you might see common implements like hand shovels and saw blades that are grotesquely crumbling into sickly brown dust as the tropical elements take their toll.
"We did an in-house test of everyday tools in four different exposure sites," explained Wong. "Some of them had very dramatic corrosion after as little as 20 days."
The extraordinarily high salt content of the air isn't the only extreme environmental element that exposed items have to contend with. When it isn't raining, the low latitude sun blazes down, and tropical insects large and small are in abundance. Yet the sturdy elevated racks the test items are affixed to have only the faintest patina of brown discoloration.
"The racks themselves are made of monel," said Wong. "They are probably 60 years old. Monel is a very corrosion-resistant metal that is quite expensive."
The nickel-copper alloy racks can hold dozens of small coupons of metal or fabric, separated from direct contact by ceramic isolators that hold them in place.
"Most of the samples are made of metal, but have different types of coating," said Wong. "We don't know the exact composition of the coating, but customers are studying which coatings can really withstand the environment."
Further, the racks can be tilted to a specific angle for customers who want their samples exposed to a certain level of direct sunlight. The items are recovered and returned to customers after a period of time that ranges from weeks to years depending on the customer's specific needs. Meteorological apparatus collect data regarding weather and chloride levels, and the testers themselves return to inspect the samples at regular intervals.
Exposure to a severe environment like this one can have consequences that a designer or manufacturer never dreamed possible. Some paints, for example, turned fluorescent after exposure, which could have drastic implications for Soldiers trying to operate clandestinely.
TRTC can conduct exposure testing on all kinds of materiel, from bullets and training rounds to sighting systems from howitzers and aircraft. Testing in tropical environments is critical to avoid unexpected operational problems with the functionality of equipment: dense jungle vegetation can sometimes interfere with chemical-biological detectors, for example, and extreme moisture can degrade body armor and even rifle cartridges.
"A lot of the folks who come to us are repeat customers," said Hugh. "The service they receive is supportive and professional in every aspect, from logistics to test writing and reporting."
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