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Auxetics advances

August 13th, 2013 / By: / Feature

An engineering and design company, Advanced Fabric Technologies focuses on developing material solutions for military and commercial applications that incorporate auxetic architecture. The unique characteristics of auxetic geometry, a negative Poisson ratio, allow a fabric to become thicker under stress rather than thinner as experienced in most fabrics. The ability to move or expand under stress creates a new platform for materials that can benefit existing systems or create new ones.

Although the company began its work in military applications, it has felt the need to diversify, as that market has been shrinking. There is, however, “big interest,” president David O’Keefe says, on the civilian side. Even a popular lingerie company has taken notice; the company is developing a new strap for the apparel maker.

“We’re constantly looking for solvable issues that an existing platform has,” O’Keefe says. “This is not a single-application geometry;  it’s a whole new platform that allows us to go in many directions.”

Defining auxetics

“It’s the yarn that we control. “By definition, an auxetic yarn is a wrapped elastomer,” he says. “Under stress we can make it move in a certain way to create a negative Poisson ratio. This movement can be controlled by the number of wraps per meter and at what angle the wrap fiber is put around the core elastomer.  Thus, the movement can be calculated to accommodate specific applications.

“What we do is manipulate that movement. When you stretch most things, they get smaller or thinner [positive Poisson ratio]. In blasts, the material actually gets fatter as it expands; that’s a negative Poisson ratio. When the yarns are lined up in a row, and they expand, it’s able to mitigate the energy without losing its integrity. That’s the baseline definition of auxetic,” O’Keefe says.

Beyond the basics

Beyond the basic platform, the engineering and design of an application decides the nature of the energy mitigation. “How much movement? What environment are you putting it into?” he says. “Once we know the specs or parameters, we can work to combine the right fibers to create a proper solution for that application,” he says. “We can come and go with any fiber group they want—usually the driver is weight and cost—what they’re after is the ability to disperse energy more efficiently than a flat-weave aramid.”

O’Keefe says they’ve used the technology to improve a tool used by an oil company. “It’s made of rubber with a steel casing. What happens is the rubber is eaten up and it blows out with pressure. They asked, ‘Can you make a better one using auxetics technology?’ Our engineers looked at it and said, ‘Yes.’ We made an auxetic ‘sock’ that’s molded into it, so it has more structural integrity.”

Smart compression socks

The company is now focusing on a new medical application, a compression sock for diabetics, or patients who are in surgery or after surgery to mitigate the danger of clotting. “But we’re making it “smart,” he says. “We’re putting sensors in it so the fabric will actually move.

“Because of our geometry and how we can manipulate the yarn, we can also create a whole new platform for compression applications. Compression socks typically are very hard to get on and off. People with arthritis or older people may not have the strength to get them on and off,” O’Keefe says.

The sock in development can go on loose and is adjusted with a battery-powered hand-held device to create the amount of pressure prescribed by the doctor. With spandex, “It is what it is,” he says. “You can adjust it by making a bigger sock, but not with regulated movement in different areas of the foot and leg. We’re going to modulate it, so you have more compression at the bottom and less on the top, and that’s what the doctors are after.” Settings can also be adjusted appropriately for each patient.

“The key to this is not having to wear [the sock] as many hours as you do now,” he says. “Currently, it takes 14 to 17 hours a day to receive the benefits of the progression, but if it’s too tight or too hot, they just won’t wear it. We want to eliminate the need to have it on that long.”

The company hopes to have a deliverable prototype by the end of the year and go directly into testing. “This time next year, we could be in the marketplace,” O’Keefe says.

Many markets, across applications

“When we do something in one field, it usually affects something in another field,” he says. Before the Sequester, The Navel Research Center wanted the company to work on improving helmets, gloves and boots. “But on the civilian side, there’s a tremendous interest in helmet design—for sports, in particular,” he says. “What that means is, whatever we find that improves a football helmet, say, can be transferred directly to the military.”

O’ Keefe noted that the acoustic trauma associated with a blast can also cause brain trauma, a specific issue that the company is working to address. They are also working with an auto racing group interested in driving suits that are “smart” and offer better protection from fire. “Technological development goes back and forth,” he says. “It will enhance existing platforms or create brand new ones. Whether it’s medical or industrial or military – it really doesn’t matter. Solutions can be spread out across all disciplines.”

David O’Keefe is president of Advanced Fabric Technologies and serves on the advisory committee for Advanced Textiles Source, IFAI’s new online publication. He will be speaking at IFAI’s Advanced Textiles Conference & Trade Show Oct. 23 on “Auxetic Engineered Designs for Industrial, Medical and Smart Textile Applications.” For more information, visit www.ifaiexpo.com.