Nanostructured material stronger than a speeding bullet
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, California, 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 materials 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.
— Read more in Jae-Hwang Lee et al., “High strain rate deformation of layered nanocomposites,” Nature Communications 3 (6 November 2012) (doi:10.1038/ncomms2166)
Reprinted with permission of MIT News
