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Saturday, October 23, 2021

Materials science on the battlefield

For American soldiers serving in Iraq and Afghanistan, experiments conducted in the labs of UC Davis might mean the difference between life and death. Researchers in the UC Davis department of materials science recently designed a superstrong aluminum alloy that could be used to strengthen the shells of military vehicles.

The researchers studied the structure of aluminum 7075, an alloy that contains 2 percent zinc and magnesium, to see if they could make it resistant to higher degrees of pressure. By analyzing the metal on a very small scale, the team found that manipulating the tiny “grains” in the metal could make it more effective against projectiles.

“If you use this material, you can improve the efficiency against projectiles by about 30 percent, which is huge,” said Enrique Lavernia, a professor of materials science, as well as provost and executive vice chancellor at UC Davis.

To understand how the superstrong alloy works, one must understand the emerging field of nanostructured materials.

Lavernia admits that a lot of people do not understand the true meaning of “nano.” He explained that 1,000,000,000 nanometers make up one meter. In terms of scale, that’s the equivalent of the length of a grain of rice to the distance from Los Angeles to New York.

Scientists working with nanostructured metals don’t just look at the chemical compounds that make up the metal – they also study the interaction between chemicals on a molecular scale. The bonds that hold together the nano-sized molecules make a difference in how the metal reacts to pressure.

When metals become solid, the molecules take on a crystalline structure – they build a sort of lattice. But, as Lavernia said, “there’s never a perfect crystal.” Structural flaws, called dislocations, occur when a column of molecules in the crystal is missing. Dislocations within the crystal make the metal weak.

Lavernia demonstrated the problem using a paper-clip. He bent the paperclip back and forth until it was close to breaking. He explained that when you bend a paperclip – or any metal object – you are adding dislocations to the crystalline structure.

“All these dislocations start getting together and forming a crack,” Lavernia said.

When looking at the nanostructure of the aluminum alloy, Lavernia and his colleagues realized that they did not have to have the natural dislocations scattered throughout the metal. Instead, they could strengthen the metal by concentrating the flaws in one tiny space.

“Instead of allowing the dislocations to form a crack, the dislocations form a grain,” Lavernia said.

Fellow researcher Julie Schoenung, professor of chemical engineering and materials science at UC Davis, described how the newly designed aluminum reacted to “high-strain tests” conducted by colleagues at Johns Hopkins University.

“We thought the samples would just fracture – just shatter under pressure, but instead they were squeezed like a pancake,” Schoenung said.

The ability of the metal to absorb pressure without breaking makes it perfect for use in the military’s armored vehicles. Schoenung said the department is currently working with the U.S. Army and Navy to make sure the metals fulfills military requirements.

Just last week, four Italian soldiers were killed in Afghanistan when their armored vehicle was hit by an improvised explosive device, reported CNN. Lavernia and Schoenung seem optimistic that their research could help reduce such casualties. The aluminum alloy not only absorbs more pressure than currently used metals, but it is lighter and more practical for use in fast-moving vehicles.

MADELINE McCURRY-SCHMIDT can be reached at science@theaggie.org.

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