In its ongoing battle to fight material degradation, the Department of Defense (DoD) Corrosion Policy and Oversight Office has enlisted several partners to expose various materials to natural, outdoor tropical regions in the Republic of Panama. Their goal is to learn how the world’s harshest jungle and ocean environments can degrade materials used for aircraft and myriad types of military equipment, as well as clothing, tent materials, and gear used by troops. Throughout this initiative, DoD’s partners include the U.K. and French defense ministries, as well as the U.S. Air Force; U.S. Marine Corps; U.S. Army Natick Soldier Research, Development, and Engineering Center; University of Akron; and Texas A&M University.
The DoD Corrosion Office is carrying out its testing and evaluation effort with the assistance of experts at the U.S. Army Yuma Proving Ground’s Tropic Regions Testing Center (TRTC). For the past four years, Army TRTC has provided test racks for test coupons, and fabric and materials for natural exposure. These test racks are located in three distinct environments in Panama—Army TRTC’s “triple canopy” forested jungle region, coastal areas, and the Marine Breakwater Exposure test site next to the ocean. Army TRTC has also installed meteorology stations in these areas to collect important environmental data.
As an institutional partner in the joint testing effort since 2015, researchers at Texas A&M University have embarked on a two-year effort to collect and analyze samples exposed to the tropics in order to create a model for accelerated salt fog testing in the laboratory that more accurately reflects what happens to materials and fabrics in highly corrosive, natural tropical environments.
“Under the aegis of the DoD Corrosion Office—which first funded our project through the University of Akron and is expected to support us under the DoD Technical Corrosion Collaboration—we intend to use our data in the field to create simple models in the laboratory that can shed light on what is happening to materials and fabrics in the environment,” says Homero Castañeda, an associate professor of materials science and engineering at Texas A&M University and overseer of the university’s National Corrosion and Materials Reliability Center.
In February 2016, Castañeda and his team at Texas A&M began analyzing four groups of materials subjected to various lengths of exposure (in bi-monthly increments) at the Army TRTC’s Horoko Test Facility near the Pacific coast, situated roughly 1,641 ft (500 m) west of the northern entrance of the Panama Canal.
“These material types include aluminum and steel samples, metallic samples coated with inorganic and organic coatings, polycarbonate and polyacrylic samples that replicate the polymers used in aircraft windshields, and a variety of fabrics used for Army clothing and tents,” says Castañeda. Technicians installed the samples on nickel alloy racks, which were mounted on polyvinyl chloride (PVC) supports facing south at a 45-degree angle.
According to details published by the Army’s Test and Evaluation Command, the Horoko Test Facility used for the Texas A&M project includes forested exposure sites, “under canopy” jungle sites that allow no sunlight penetration, and open areas. The annual average temperature in this region is 81 °F (27 °C) and the temperature ranges from 77 to 88 °F (25 to 31 °C). The annual average relative humidity (RH) is 85%, and the RH ranges from 47 to 100%. The annual average rainfall is 77 in (2 m), with an average of 142 days of rain and drizzle per year.
Every two months, Castañeda’s team retrieves samples from the natural outdoor exposure test sites in Panama. Their analysis of these samples will eventually be compared to similar samples that will undergo exposure testing under laboratory conditions. “After two years of analyzing our samples, we plan to build a simple mathematical model for the lab based on all of our materials, which will characterize the harsh, corrosive conditions in the field,” Castañeda explains. “We plan to use this model to correlate accelerated exposure testing in an environmental testing chamber on campus.”
Through his team’s testing and evaluation, Castañeda’s ultimate goal is to create a more dynamic corrosion map that measures weather and atmospheric conditions over time and links them with corrosivity. His dynamic corrosion map will indicate how corrosivity changes with time, based on factors such as rain, temperature, and humidity and how they each vary relative to one another. “Currently the corrosion maps that exist online are not time dependent, and do not indicate how the corrosivity of atmospheric conditions can change over time,” he says.
Castañeda further explains: “One of our key goals is to create an environmental testing protocol in the lab that can conduct a better-calibrated lab testing procedure, compared to the current standard test procedure, that is achieved using a salt spray cabinet (often specified in ASTM B1171). Over the long-term we want to investigate how we might change the electrolyte and salt fog environment that govern standards such as ASTM B117, and thereby create a new standard for accelerated lab testing that mimics true tropical field conditions in real time.”
“Most importantly, we are trying to simulate tropical environmental conditions in the lab, while also creating trends in the lab to understand what’s happening in the environment,” Castañeda says. “Doing so will create a tool that will help to predict and characterize the environment in which DoD assets will be used or stored, permitting the preservation of such assets under reliable operation conditions.”
Because it is incumbent on United States troops to operate effectively within the harshest environments, the DoD Corrosion Office is committed to better understanding the science of corrosion and material degradation in the tropics. According to Army experts, numerous factors in the world’s jungle regions—heat, humidity, and rainfall, as well as bacteria, fungus, insects, and solar radiation—conspire to hinder the warfighters’ missions.
“Our tradition of recreating artificial environments in testing chambers is useful, but the work of Texas A&M researchers will allow us to better understand how all factors of degradation combine in order to create better-quality materials impervious to degradation in tropical regions,” says Rich Hays, deputy director of the DoD Corrosion Office.”
Source: This article was written by Cynthia Greenwood, outreach & communications liaison with the DoD Corrosion Policy and Oversight Office.
1 ASTM B117-16, “Standard Practice for Operating Salt Spray (Fog) Apparatus” (West Conshohocken, PA: ASTM International, 2016).