New material

Article 1: Ultralight "Super-Material" is 10 times stronger than steel. 

By Tia Ghose, Senior Writer

A spongy new super-material could be lighter than the flimsiest plastic yet 10 times stronger than steel.

The new super-material is made up of flecks of graphene squished and fused together into a vast, cobwebby network. The fluffy structure, which looks a bit like a psychedelic sea creature, is almost completely hollow; its density is just 5 percent that of ordinary graphene, the researchers said.

What's more, though the researchers used graphene, the seemingly magical properties of the material do not totally depend on the atoms used: The secret ingredient is the way those atoms are aligned, the scientists said.

"You can replace the material itself with anything," Markus J. Buehler, a materials scientist at the Massachusetts Institute of Technology (MIT) said in a statement. "The geometry is the dominant factor. It's something that has the potential to transfer to many things."

Graphene, a material made up of flaky sheets of carbon atoms, is the strongest material on Earth — at least in 2D sheets. On paper, ultrathin sheets of graphene, which are just an atom thick, have unique electrical properties and indomitable strength. Unfortunately, these properties don't easily translate to 3D shapes that are used to build things. [7 Technologies That Transformed Warfare]

Past simulations suggested that orienting the graphene atoms a specific way could enhance strength in three dimensions. However, when researchers tried to create these materials in the lab, the results were often hundreds or thousands of times weaker than predicted, the researchers said in the statement. 

Stronger than steel

To address this challenge, the team got down to basics: analyzing the structure at the atomic level. From there, the researchers created a mathematical model that can accurately predict how to create remarkably strong super-materials. The researchers then used precise amounts of heat and pressure to produce the resulting curvy, labyrinthine structures, known as gyroids, which were first mathematically described by a NASA scientist in 1970.

"Actually making them using conventional manufacturing methods is probably impossible," Buehler said.

The material's strength comes from its enormous surface-area-to-volume ratio, the researchers reported in a study published Jan. 6 in the journal Science Advances. In nature, sea creatures like coral and diatoms also leverage a large surface-area-to-volume ratio to achieve incredible strength at tiny scales.

"Once we created these 3D structures, we wanted to see what's the limit — what's the strongest possible material we can produce," study co-author Zhao Qin, a civil and environmental engineering researcher at MIT, said in the statement.

The scientists created a series of models, built them, and then subjected them to tension and compression. The strongest material the researchers created was about as dense as the lightest plastic bag, yet stronger than steel.

One obstacle to creating these superstrong materials is the lack of industrial manufacturing capability for producing them, the researchers said. However, there are ways the material could be produced at larger scales, the scientists said

For instance, the actual particles could be used as templates that are coated with graphene through chemical vapor deposition; the underlying template could then be eaten or peeled away using chemicals or physical techniques, leaving the graphene gyroid behind, the researchers said.

In the future, massive bridges could be made of gyroid concrete, which would be ultrastrong, lightweight, and insulated against heat and cold because of all the myriad air pockets in the material, the researchers said.

Article 2 : Metallic Foams annihilate bullets, block radiation

By Nathaniel Scharping

The word foam doesn’t necessarily convey strength, but seeing a bullet explode upon impact with composite metal foam certainly does.

Researchers at North Carolina State University created a bubble-filled metal composite that combines the strength of steel with the airiness and heat-resistant properties of foam. In tests with armor-piercing bullets, a one-inch layer of the material stopped the projectile in its tracks while allowing only an 8-millimeter indentation on the other side. Afsaneh Rabiei, a professor of mechanical and aerospace engineering at North Carolina State University, claims her version of metallic foam is the strongest yet.

The Secret is the Bubbles

Foams are made mostly of air pockets — that’s what makes them so light. They derive their strength from the composition and structure of the material that surrounds the air pockets, a steel alloy in this case. Rabiei has worked with composite metal foams (CMFs) for years to understand their unique properties and find the optimal configuration of materials and bubbles to maximize results.  

“If you look around, you will see a ton of porous materials in nature: wood, bone, leaves, a bird’s wings, anything that you want to be lightweight or have cushionability, you’ll see that it has air bubbles,” says Rabiei. “It’s a waste of material and energy to carry a solid bulk of materials with you, when you can actually use something much lighter and accomplish even more.”

n her latest study, published in the International Journal of Thermal Sciences, Rabiei describes two different methods of making her metal foam, both of which rely on hollow steel spheres to form the “bubbles.” The first method casts a metal with a low melting point, like aluminum, around the spheres, creating a matrix of hollow spaces within. For metals with higher melting points, the spheres are packed in by a metal powder that is compressed in a process called sintering to form a solid.

It Can Take the Heat

But it all comes down to the bubbles, says Rabiei. By keeping the diameter of the spheres constant, she says, any stress will impact them equally, increasing the material’s strength. The spherical shape of the bubbles confers strength as well, by distributing the force evenly around the structure. Where other metal foams buckle as their bubbles collapse, Rabiei’s maintains its structure thanks to the uniform nature of the components.

Because the spheres are filled with air, the material is also resistant to heat and heat-related expansion. In her latest experiment, she compared a block of solid stainless steel to the bubble-infused steel as both were heated by an 800-degree flame on one side. The CMF took twice as long to reach 800 degrees as the solid block, a result of the air-filled bubbles inside.

Putting CMFs to Work

The unique properties of CMFs make them ideal for use in body armor, as the bullet demonstration makes plain. Rabiei also sees uses for them in the space industry, where lightweight, durable materials are in high demand.

Additionally, by adding tungsten and vanadium to the composite, Rabiei says her CMF blocks radiation, including gamma rays, X-rays and neutron radiation. This makes the material ideal for transporting nuclear waste, she says, and also increases its utility for space travel, where harmful radiation poses a danger to human health.

In the future, Rabiei would like to test how well her metal foam stands up to vibrations, a property that could carry further benefits for vehicle construction dampen sound-proofing. Ultimately, her end game is to save a person’s life.

“If I can make one person walk out of an accident because of my materials, I will have accomplished my goal,” she says.

Resume :

As these two articles show, research on new subjects is increasingly being pursued.

The goal is to find materials increasingly lighter and more and more resistant and strong. The constructions made of stone and concrete are solid, of course, but these materials are suspended over time, which is why the material put forward in the first article is in full development.

In addition, new materials could be used to defend themselves as set out in article two. The development of this process could lead us to new means of protection.