What if a helmet could be programmed to direct collision impact to regions far from the skull while being a lighter-weight material?

What if body armor could suddenly transform into a state that can disperse greater impact when hit by a bullet, while being flexible in regular conditions?

A team of researchers led by the University of Michigan is looking to develop just that type of material using a five-year, $7.5 million grant from the Office of Naval Research, as part of the Department of Defense’s 2020 Multidisciplinary University Research Initiative program.

Xiaoming Mao, associate professor of physics in LSA, received the grant to bring her theoretical work of turning a kind of metamaterial the physical properties of which are changeable from the nanoscale to the macroscale.

Mao studies metamaterials, a type of material that gets its properties from the way the material is structured rather than the material itself. This means that, using the right method, the material can be constructed to have the particular property desired.

In this case, Mao has been designing a metamaterial that changes properties based on how an object comes into contact with it.

When an object comes in contact with the edge of this metamaterial, it changes the geometry of the material’s structure and quickly transforms its ability to carry stress and respond to forces. This allows a piece of solid material to absorb shock, direct stress and help prevent damage.

“For cars, you can easily imagine that if you change the material’s surface between the stiffness of a metal and the softness of rubber, that could be very useful in collision protection,” Mao said. “These materials may have applications in defense, where it could be used to design helmets and armor.”

The research team will use the grant to verify its method — originally published in a 2017 study in Nature Communications — in two ways: by using 3-D printing and by using self-assembling building blocks.

Team member Ellen Arruda will use her expertise in 3-D printing to print the material at the macroscale. Arruda is the Maria Comninou Collegiate Professor of Mechanical Engineering, professor of mechanical engineering, biomedical engineering, and macromolecular science and engineering.

Engineering professors Nicholas Kotov of U-M and Qian Chen of the University of Illinois will use their expertise in designing building blocks that can self-assemble into any structure, which will create the material at the nanoscale. Kotov is the Joseph B. and Florence V. Cejka Professor of Engineering, professor of chemical engineering, materials science and engineering, and macromolecular science and engineering.

Other researchers include Kai Sun, associate professor of physics at U-M, and engineer Zi Chen of Dartmouth College.

The team will closely collaborate, bringing together expertise from physics, materials science, mechanical engineering and chemistry, aiming at realizing these transformable metamaterials with unprecedented mechanical properties.