Developing Flexible Metal Composite

"The use of shape memory alloys is very attractive because it enables large global recoverable, super-elastic deformations of up to six percent, a ten-fold over conventional elastic response. We hope to elicit even greater super-elastic performance by creating a hybrid composite alloy material" says Sia Nemat-Nasser, director of the Center of Excellence for Advanced Materials and principal investigator for the project.

Although shape-memory alloys have been around for over 30 years, Nemat-Nasser and his colleagues are adding a new spin by combining them with other non-metallic materials. He is working with Kenneth Vecchio, a professor of materials science at the School, and representatives from Caltech and the University of Washington, to use plates of shape-memory nickel-titanium (Ni-Ti) to sandwich shape-memory, super-elastic foams and rods embedded with hollow glass beads.

"This unique combination should allow for even greater flexibility and resilience in a very lightweight structure," explains Nemat-Nasser. "The hybrid material should provide optimal energy absorbing capability against high-velocity projectile impact, explosion-induced shock, or other dynamic events." In other words, the absorbing capability, in conjunction with the material's flexibility, could enable it to stop cracks and collateral damage by distributing the forces from impact.

To test the new alloy composite, Nemat-Nasser and his coworkers will use a variety of devices, including a full complement of novel Hopkinson bars, gas guns, high-speed cameras, and high-speed X-ray machines, as well other common materials processing and characterization equipment.

Nemat-Nasser is a member of the National Academy of Engineering (NAE), and most recently received the 2002 William Prager and Nadai Medals.