Tag Archives: body armor

Ooblek (non-Newtonian goo) and bras from Reebok

I have taken a liberty in the title for this piece, strictly speaking the non-Newtonian goo in the bra isn’t the stuff (ooblek) made of cornstarch and water from your childhood science experiments but it has many of the same qualities. The material in the Reebok bra, PureMove, is called Shear Thickening Fluid and was developed at the University of Delaware in 2005 and subsequently employed by NASA (US National Aeronautics and Space Administration) for use in the suits used by astronauts as noted in an August 6, 2018 article by Elizabeth Secgran for Fast Company who explains how it came be used for the latest sports bra,

While the activewear industry floods the market with hundreds of different sports bras every season, research shows that most female consumers are unsatisfied with their sports bra options, and 1 in 5 women avoid exercise altogether because they don’t have a sports bra that fits them properly.

Reebok wants to make that experience a thing of the past. Today, it launches a new bra, the PureMove, that adapts to your movements, tightening up when you’re moving fast and relaxing when you’re not. …

When I visited Reebok’s Boston headquarters, Witek [Danielle Witek, Reebok designer who spearheaded the R&D making the bra possible] handed me a jar of the fluid with a stick in it. When I moved the stick quickly, it seemed to turn into a solid, and when I moved it slowly, it had the texture of honey. Witek and the scientists have incorporated this fluid into a fabric that Reebok dubs “Motion Sense Technology.” The fluid is woven into the textile, so that on the surface, it looks and feels like the synthetic material you might find in any sports bra. But what you can’t see is that the fabric adapts to the body’s shape, the velocity of the breast tissue in motion, and the type and force of movement. It stretches less with high-impact movements and then stretches more during rest and lower intensity activities.

I tested an early version of the PureMove bra a few months ago, before it had even gone into production. I did a high-intensity workout that involved doing jumping jacks and sprints, followed by a cool-down session. The best thing about the bra was that I didn’t notice it at all. I didn’t feel stifled when I was just strolling around the gym, and I didn’t feel like I was unsupported when I was running around. Ultimately, the best bras are the ones that you don’t have to think about so you can focus on getting on with your life.

Since this technology is so new, Reebok had to do a lot of testing to make sure the bra would actually do what it advertised. The company set up a breast biomechanics testing center with the help of the University of Delaware, with 54 separate motion sensors tracking and measuring various parts of a tester’s chest area. This is a far more rigorous approach than most testing facilities in the industry that typically only use between two to four sensors. Over the course of a year, the facility gathered the data required for the scientists and Reebok product designers to develop the PureMove bra.

… If it’s well-received, the logical next step would be to incorporate the Motion Sense Technology into other products, like running tights or swimsuits, since transitioning between compression and looseness is something that we want in all of our sportswear. ..

According to the Reebok PureMove bra webpage, it was available from August 16, 2018,

Credit: Reebok

It’s $60 (I imagine those are US dollars).

For anyone interested in the science of non-Newtonian goo, shear thickening fluid, and NASA, there’s a November 24, 2015 article by Lydia Chain for Popular Science (Note: Links have been removed),

There’s an experiment you may have done in high school: When you mix cornstarch with water—a concoction colloquially called oobleck—and give it a stir, it acts like a liquid. But scrape it quickly or hit it hard, and it stiffens up into a solid. If you set the right pace, you can even run on top of a pool of the stuff. This phenomenon is called shear force thickening, and scientists have been trying to understand how it happens for decades.

There are two main theories, and figuring out which is right could affect the way we make things like cement, body armor, concussion preventing helmets, and even spacesuits.

The prevailing theory is that it’s all about the fluid dynamics (the nature of how fluids move) of the liquid and the particles in a solution. As the particles are pushed closer and closer together, it becomes harder to squeeze the liquid out from between them. Eventually, it’s too hard to squeeze out any more fluid and the particles lock up into hydrodynamic clusters, still separated by a thin film of fluid. They then move together, thickening the mixture and forming a solid.

The other idea is that contact forces like friction keep the particles locked together. Under this theory, when force is applied, the particles actually touch. The shearing force and friction keep them pressed together, which makes the solution more solid.

“The debate has been raging, and we’ve been wracking our brains to think of a method to conclusively go one way or the other,” says Itai Cohen, a physicist at Cornell University. He and his team recently ran a new experiment that seems to point to friction as the driving cause of shear thickening.

Norman Wagner, a chemical engineer at the University of Delaware, says that research into frictional interactions like this is important, but notes that he isn’t completely convinced as Cohen’s team didn’t measure friction directly (they inferred it was friction from their modeling however they didn’t find the exact measurement of the friction between the particles). He also says that there’s a lot of data in the field already that strongly indicates hydrodynamic clusters as the cause for shear thickening.

Wagner and his team are working on a NASA funded project to improve space suits so that micrometeorites or other debris can’t puncture them. They have also bent their technology to make padding for helmets and shin guards that would do a better job protecting athletes from harmful impacts. They are even making puncture resistant gloves that would give healthcare workers the same dexterity as current ones but with extra protection against accidental needle sticks.

“It’s a very exciting area,” says Wagner. He’s very interested in designing materials that automatically protect someone, without robotics or power. …

I guess that in 2015 Wagner didn’t realize his work would also end up in a 2018 sports bra.

The inside scoop on beetle exoskeletons

In the past I’ve covered work on the Namib beetle and its bumps which allow it to access condensation from the air in one of the hottest places on earth and work on jewel beetles and how their structural colo(u)r is derived. Now, there’s research into a beetle’s body armor from the University of Nebraska-Lincoln according to a Feb. 22, 2017 news item on ScienceDaily,

Beetles wear a body armor that should weigh them down — think medieval knights and turtles. In fact, those hard shells protecting delicate wings are surprisingly light, allowing even flight.

Better understanding the structure and properties of beetle exoskeletons could help scientists engineer lighter, stronger materials. Such materials could, for example, reduce gas-guzzling drag in vehicles and airplanes and reduce the weight of armor, lightening the load for the 21st-century knight.

But revealing exoskeleton architecture at the nanoscale has proven difficult. Nebraska’s Ruiguo Yang, assistant professor of mechanical and materials engineering, and his colleagues found a way to analyze the fibrous nanostructure. …

A Feb. 22, 2017 University of Nebraska-Lincoln news release by Gillian Klucas (also on EurekAlert), which originated the news item, describes skeletons and the work in more detail,

The lightweight exoskeleton is composed of chitin fibers just around 20 nanometers in diameter (a human hair measures approximately 75,000 nanometers in diameter) and packed and piled into layers that twist in a spiral, like a spiral staircase. The small diameter and helical twisting, known as Bouligand, make the structure difficult to analyze.

Yang and his team developed a method of slicing down the spiral to reveal a surface of cross-sections of fibers at different orientations. From that viewpoint, the researchers were able to analyze the fibers’ mechanical properties with the aid of an atomic force microscope. This type of microscope applies a tiny force to a test sample, deforms the sample and monitors the sample’s response. Combining the experimental procedure and theoretical analysis, the researchers were able to reveal the nanoscale architecture of the exoskeleton and the material properties of the nanofibers.

Yang holds a piece of the atomic force microscope used to measure the beetle's surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

Craig Chandler | University Communication

Yang holds a piece of the atomic force microscope used to measure the beetle’s surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

They made their discoveries in the common figeater beetle, Cotinis mutabilis, a metallic green native of the western United States. But the technique can be used on other beetles and hard-shelled creatures and might also extend to artificial materials with fibrous structures, Yang said.

Comparing beetles with differing demands on their exoskeletons, such as defending against predators or environmental damage, could lead to evolutionary insights as well as a better understanding of the relationship between structural features and their properties.

Yang’s co-authors are Alireza Zaheri and Horacio Espinosa of Northwestern University; Wei Gao of the University of Texas at San Antonio; and Cheryl Hayashi of the University of California, Riverside.

Here’s a link to and a citation for the paper,

Exoskeletons: AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties by Ruiguo Yang, Alireza Zaheri,Wei Gao, Charely Hayashi, Horacio D. Espinosa. Adv. Funct. Mater. vol. 27 (6) 2017 DOI: 10.1002/adfm.201770031 First published: 8 February 2017

This paper is behind a paywall.

Hairy strength could lead to new body armour

A Jan. 18, 2017 news item on Nanowerk announces research into hair strength from the University of California at San Diego (UCSD or UC San Diego),

In a new study, researchers at the University of California San Diego investigate why hair is incredibly strong and resistant to breaking. The findings could lead to the development of new materials for body armor and help cosmetic manufacturers create better hair care products.

Hair has a strength to weight ratio comparable to steel. It can be stretched up to one and a half times its original length before breaking. “We wanted to understand the mechanism behind this extraordinary property,” said Yang (Daniel) Yu, a nanoengineering Ph.D. student at UC San Diego and the first author of the study.

A Jan. 18 (?), 2017 UCSD news release, which originated the news item, provides more information,

“Nature creates a variety of interesting materials and architectures in very ingenious ways. We’re interested in understanding the correlation between the structure and the properties of biological materials to develop synthetic materials and designs — based on nature — that have better performance than existing ones,” said Marc Meyers, a professor of mechanical engineering at the UC San Diego Jacobs School of Engineering and the lead author of the study.

In a study published online in Dec. in the journal Materials Science and Engineering C, researchers examined at the nanoscale level how a strand of human hair behaves when it is deformed, or stretched. The team found that hair behaves differently depending on how fast or slow it is stretched. The faster hair is stretched, the stronger it is. “Think of a highly viscous substance like honey,” Meyers explained. “If you deform it fast it becomes stiff, but if you deform it slowly it readily pours.”

Hair consists of two main parts — the cortex, which is made up of parallel fibrils, and the matrix, which has an amorphous (random) structure. The matrix is sensitive to the speed at which hair is deformed, while the cortex is not. The combination of these two components, Yu explained, is what gives hair the ability to withstand high stress and strain.

And as hair is stretched, its structure changes in a particular way. At the nanoscale, the cortex fibrils in hair are each made up of thousands of coiled spiral-shaped chains of molecules called alpha helix chains. As hair is deformed, the alpha helix chains uncoil and become pleated sheet structures known as beta sheets. This structural change allows hair to handle a large amount deformation without breaking.

This structural transformation is partially reversible. When hair is stretched under a small amount of strain, it can recover its original shape. Stretch it further, the structural transformation becomes irreversible. “This is the first time evidence for this transformation has been discovered,” Yu said.

“Hair is such a common material with many fascinating properties,” said Bin Wang, a UC San Diego PhD alumna from the Department of Mechanical and Aerospace Engineering and co-author on the paper. Wang is now at the Shenzhen Institutes of Advanced Technology in China continuing research on hair.

The team also conducted stretching tests on hair at different humidity levels and temperatures. At higher humidity levels, hair can withstand up to 70 to 80 percent deformation before breaking (dry hair can undergo up to 50 percent deformation). Water essentially “softens” hair — it enters the matrix and breaks the sulfur bonds connecting the filaments inside a strand of hair. Researchers also found that hair starts to undergo permanent damage at 60 degrees Celsius (140 degrees Fahrenheit). Beyond this temperature, hair breaks faster at lower stress and strain.

“Since I was a child I always wondered why hair is so strong. Now I know why,” said Wen Yang, a former postdoctoral researcher in Meyers’ research group and co-author on the paper.

The team is currently conducting further studies on the effects of water on the properties of human hair. Moving forward, the team is investigating the detailed mechanism of how washing hair causes it to return to its original shape.

Here’s a link to and a citation for the paper,

Structure and mechanical behavior of human hair by Yang Yua, Wen Yang, Bin Wang, Marc André Meyers. Materials Science and Engineering: C Volume 73, 1 April 2017, Pages 152–163    http://dx.doi.org/10.1016/j.msec.2016.12.008

This paper is behind a paywall.