New tests of nanostructured material could lead to better armor

Nov 07, 2012 by David L. Chandler
New tests of nanostructured material could lead to better armor
This electron-microscope image of a cross-section of a layered polymer shows the crater left by an impacting glass bead, and the deformation of the previously even, parallel lines of the layered structure as a result of the impact. In this test, the layered material was edge-on to the impact. Comparative tests showed that when the projectile hit head-on, the material was able to resist the impact much more effectively. Credit: Thomas Lab, Rice University

Providing protection against impacts from bullets and other high-speed projectiles is more than just a matter of brute strength. While traditional shields have been made of bulky materials such as steel, newer body armor made of lightweight material such as Kevlar has shown that thickness and weight are not necessary for absorbing the energy of impacts. Now, a new study by researchers at MIT and Rice University has shown that even lighter materials may be capable of doing the job just as effectively.

The key is to use composites made of two or more materials whose stiffness and flexibility are structured in very specific ways—such as in alternating layers just a few nanometers thick. The research team produced miniature high-speed and measured the effects they had on the impact-absorbing material.

The results of the research are reported in the journal Nature Communications, in a paper co-authored by former postdoc Jae-Hwang Lee, now a research scientist at Rice; postdoc Markus Retsch; graduate student Jonathan Singer; Edwin Thomas, a former MIT professor who is now at Rice; graduate student David Veysset; former graduate student Gagan Saini; former postdoc Thomas Pezeril, now on the faculty at Université du Maine, in Le Mans, France; and chemistry professor Keith Nelson. The experimental work was conducted at MIT's Institute for Soldier Nanotechnologies.

The team developed a self-assembling polymer with a layer-cake structure: rubbery layers, which provide resilience, alternating with glassy layers, which provide strength. They then developed a method for shooting at the material at high speed by using a laser pulse to rapidly evaporate a layer of material just below its surface. Though the beads were tiny—just millionths of a meter in diameter—they were still hundreds of times larger than the layers of the polymer they impacted: big enough to simulate impacts by larger objects, such as bullets, but small enough so the effects of the impacts could be studied in detail using an electron microscope.

Seeing the layers

Structured polymer composites have previously been tested for possible impact-protection applications. But nobody had found a way to study exactly how they work—so there was no way to systematically search for improved combinations of materials.

The new techniques developed by the MIT and Rice researchers could provide such a method. Their work could accelerate progress on materials for applications in body and vehicle armor; shielding to protect satellites from micrometeorite impacts; and coatings for jet engine turbine blades to protect from high-speed impacts by sand or ice particles.

The methods the team developed for producing laboratory-scale high-speed impacts, and for measuring the impacts' effects in a precise way, "can be an extremely useful quantitative tool for the development of protective nanomaterials," says Lee, the lead author of the paper, who did much of this research while in MIT's Department of Materials Science and Engineering. "Our work presents some valuable insights to understand the contribution" of the nanoscale structure to the way such materials absorb an impact, he says.

Because the layered material has such a predictable, ordered structure, the effects of the impacts are easily quantified by observing distortions in cross-section. "If you want to test out how ordered systems will behave," Singer says, "this is the perfect structure for testing."

Which direction works best

The team found that when the projectiles hit the layers head-on, they absorbed the impact 30 percent more effectively than in an edge-on impact. That information may have immediate relevance for the design of improved protective materials.

Nelson has spent years developing techniques that use laser pulses to observe and quantify nanoscale shockwaves—techniques that were adapted for this research with the help of Lee, Veysset and other team members. Ideally, in future research, the team hopes to be able to observe the passage of projectiles in real time in order to get a better understanding of the sequence of events as the impacted material undergoes distortion and damage, Nelson says.

In addition, now that the experimental method has been developed, the researchers would like to investigate different materials and structures to see how these respond to impacts, Nelson says: varying the composition and thickness of layers, or using different structures.

Donald Shockey, director of the Center for Fracture Physics at SRI International, a nonprofit research institute in Menlo Park, Calif., says, "It's a novel and useful approach that will provide needed understanding of the mechanisms governing how a projectile penetrates protective vests and helmets." He adds that these results "provide the data required to develop and validate computational models" to predict the behavior of impact-protection materials and to develop new, improved materials.

"The key to developing with better impact resistance is to understand deformation and failure behavior at the tip of an advancing projectile," Shockey says. "We need to be able to see that."

The work was supported by the U.S. Army Research Office.

Explore further: Thinnest feasible nano-membrane produced

More information:

Related Stories

Better, stronger, lighter armor

May 22, 2012

What makes a piece of armor effective? Sure, it needs to be strong, and it should be lightweight. But what is it about a material's composition that gives it such properties? And can we develop materials that ...

New family of composite structures

Jan 13, 2012

Material scientists at ETH-Zürich are working on composite materials that mimic the structure of seashells. Such complex structures are produced using tiny magnetic particles which guide the composites' ...

Recommended for you

Thinnest feasible nano-membrane produced

Apr 17, 2014

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

Apr 17, 2014

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Making 'bucky-balls' in spin-out's sights

Apr 16, 2014

( —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...

User comments : 0

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...