U.S. Army Soldier Systems Center-Natick
Public Affairs Office
Natick, MA 01760-5012
Contact: Chief, Public Affairs Office
Date: March 12, 2001
Metallic Models Assist Researchers
Testing clothing items that enable warfighters to function in harsh environments starts at the U.S. Army Research Institute of Environmental Medicine (USARIEM) Biophysics and Biomedical Modeling Division.
USARIEM, an installation partner of the U.S. Army Soldier Systems Center (Natick), assists Natick's project officers by measuring the thermal and water vapor resistance properties of textiles, boots, gloves, clothing ensembles and sleeping bags using sophisticated metallic models. Researchers can compare the values from commercial and prototype items with those from the comparable standard military issue and quickly eliminate from the testing program those that are inferior. This rapid down-selection saves money by reducing the number of test systems when the research program also includes costly human research volunteer evaluations.
"From a biophysical standpoint, you can quickly tell whether it's simply advertising hype or truly worth further Army interest," said Tom Endrusick, research physical scientist at the Biophysics and Biomedical Division, which has tested hundreds of uniforms, boots and gloves among other products.
He said many items on the commercial market have vague or misleading protective and temperature comfort claims, mainly because the human testing required for scientifically accurate labeling is difficult and expensive. Through science, USARIEM helps ensure that the new items adopted by the Army will protect the warfighter as intended.
The division uses a variety of equipment designed specifically to ferret out the good from the bad. The Extreme Cold Weather Clothing System, Joint Service Lightweight Integrated Suit Technology, Intermediate Cold Wet Boot, Intermediate Cold Wet Glove and the Modular Sleeping Bag System are just a sample of Natick products that were screened through the modeling division. High-technology textile materials, such as Thinsulate, Polartec fleece and Gore-Tex, have also proven their effectiveness under scientific scrutiny.
Basic textile evaluation begins with the Hohenstein Thermoregulatory Model of the Human Skin. The thermal and water vapor resistances of materials intended to improve the performance of clothing systems are measured.
"Everything in nature has an inherent resistance to the flow of heat and moisture," Endrusick said. "Clothing insulation, like insulation in the walls of a home, is measured in mathematical units. The development of any new military clothing item should include an analysis of the material resistances and how they compare to those used in currently issued items intended for similar end-use."
The Hohenstein is a wettable, centrally-heated flat plate, controlled at a set temperature, and guarded below and at the sides by other heated elements maintained at the same temperature. Heated flat plates are used to measure thermal and water vapor resistances of a given fabric by calculating the power required to maintain the plate at a constant temperature under a controlled set of environmental conditions.
It works by placing a sample of test fabric on the plate inside an oven-like chamber. A constant temperature, humidity and wind speed is maintained over the sample while a computer calculates the results. Results are calculated in accordance with equations from an international standard.
After Hohenstein testing, promising materials can then be used in the fabrication of prototype clothing, gloves or boots. USARIEM has hand and foot models in order to assess the thermal resistance of items that protect the human extremities.
The sectional copper hand is an articulated aluminum device with nine thermally isolated sections used to analyze dry heat exchange and insulative properties of all types of gloves.
A pair of copper feet, each with 27 separate measuring sections, are controlled by an automatically regulated power supply, which is controlled by a microprocessor that adjusts the temperature levels of each of the sections. The feet are used to study wet and dry insulation values of all types of footwear.
"These are important because the models are anatomically-correct," Endrusick said. "The human hand and foot have large surface areas and have a high potential for injury during cold exposure. We can get values of the overall boot or glove, or isolate the areas that are at most risk, such as the fingertips or toes."
The glove or boot is slipped onto the appropriate model and then placed into an airtight, temperature and humidity-controlled chamber. He said it takes a day to measure the thermal resistance value. Using data from the foot or hand models generated from a series of improved prototypes, you can literally build a better boot or glove.
Bringing all the human factors together, the articulated copper manikin takes testing to the next level. Part of a collection of seven USARIEM manikins, the articulated manikin is divided into 19 separate zones that are also capable of being heated and monitored independently.
Endrusick said the articulated manikin is more realistic because soldiers will be moving in their clothing, and here researchers can introduce water to the manikin's skin to imitate sweating.
All sections and joints are built of electro-deposited copper with a 2.4 mm uniform thickness except at feet, hands and joints, which are cast of hard-coated aluminum. An advantage of the articulated manikin is that it can simulate a soldier marching up to 3.5 mph, which allows for the study of thermal and moisture exchanges within the clothing layers that are associated with human movement. The manikin also operates in a climate-controlled chamber with a wall of fans acting as wind.
Researchers can evaluate heat transfer and moisture flow, and the convective and radiative heat flow of newly-developed military clothing items.
"This allows you to evaluate whole clothing ensembles and study the dynamics of the microclimate between clothing and skin," Endrusick said.
If test products show superior performance through all biophysical testing and meet other important Natick performance criteria, testing often continues in both climatic chamber and field settings using human volunteers. Endrusick said information from the manikins is also helpful in one other important way. Thermal and water vapor resistances of military clothing ensembles become important mathematical coefficients in USARIEM physiological models, which can predict cold and heat stress, safe work/rest times, hydration requirements and environmental casualty rates.
Thermal manikins first developed during World War II
Thermal manikins in various levels of sophistication have existed for decades.
Legend has it that Dr. Harwood Belding, a young researcher conducting studies on heated flight suits for the Army at the Harvard Fatigue Laboratory in the early 1940s, saw a window manikin in a Boston department store and was inspired to build his own. Belding's first heated manikin was constructed out of stovepipe and sheet metal by a Boston tinsmith.
"It looked like the Michelin Man, but it was theoretically similar to the thermal manikins used worldwide today," said Tom Endrusick, a research physical scientist at the U.S. Army Research Institute of Environmental Medicine (USARIEM).
In 1941, the actual scientific study of military clothing started because the War Department was concerned about the inadequacies of military clothing at the beginning of World War II, according to Endrusick.
The urgency to develop better clothing hit home in May 1943 when 2,100 of the 15,000 U.S. troops who were sent to retake the Japanese-occupied Aleutian Island of Attu suffered from trench foot and cold exposure. They were wearing wool and cotton clothing along with uninsulated leather boots that were developed during World War I.
Belding's stovepipe manikin provided the first useful biophysical data related to a military clothing ensemble and brought him in contact with researchers at General Electric in Bridgeport, Conn.
He asked GE to build him a manikin made of copper like the one that the company was using to develop the first heated blankets for consumers. GE eventually delivered a series of four copper manikins as well as the first copper hand and foot to the Army.
As World War II continued, the Army and the other services intensified their efforts to develop better military clothing. In 1943, the U.S. Army Quartermaster Corps formed the Climatic Research Laboratory (CRL) and moved it into the Pacific Woolen Mills facility in Lawrence, Mass.
In 1945, Belding brought his manikin and expertise with him when he became the first civilian director of the CRL. That lab was reorganized as the Environmental Protection Research Division (EPRD), which became part of the new Quartermaster Research and Development Command at Natick in 1954. EPRD joined with elements of the Armored Medical Research Laboratory at Fort Knox, Ky., to form USARIEM in 1961.
Endrusick said many of the first generation metallic models still exist but are in storage. Models still in service are upgraded, rebuilt and refurbished about every 10-15 years as technology advances. He said the basic clothing research conducted during the early 1940's eventually formed the foundation for much of the work that is now conducted at the U.S. Army Soldier Systems Center (Natick).
"Soldiers were fighting in environments never encountered before World War II," Endrusick said. "They were required to operate in severe climatic extremes. Today's soldiers are facing the same extremes, and that's why we continue to provide the support for this research that started over a half century ago."
Natick is part of the U.S. Army Soldier and Biological Chemical Command (SBCCOM). For more information about SBCCOM or the Soldier Systems Center (Natick), please visit our web site at http://www.sbccom.army.mil.