December 11, 2012 | 2
When a high speed object collides with force, we tend to focus on the spectacular (yet potentially devastating) view from a macro scale, but Duke scientists have been researching what that incredible energy transfer looks like at the level of sand and dirt size particles.
“High-speed video of projectiles slamming into a bed of disks has given scientists a new microscopic picture of the way a meteorite or missile transfers the energy of its impact to sand and dirt grains.
The transfer is jerky, not smooth. “It was surprising just how unsmooth the slow-down of the intruding object was,” Duke physicist Robert Behringer said. His team describes their new videos and impact analysis in the Dec. 7 Physical Review Letters. The research may change the way scientists model meteorite and missile impacts and their effects.”
Take a look at the video from their work:
“Scientists previously assumed that the slowing down would be smooth and that any sound wave would travel through a granular material in a regular, uniform pattern, similar to the way noise from a clap of the hands diffuses evenly in all directions through the air. But using high-speed video, Behringer, his graduate student Abram Clark and Lou Kondic of the New Jersey Institute of Technology have shown a very different behavior for the sound wave and grains during a collision.
In the study, supported by the Defense Threat Reduction Agency, the team shot bronze disks into a narrow bed of photoelastic grains and used an ultrafast camera to track the collision energy as it shifted from the disk to the beads. The footage shows that the bronze disk loses most of its energy in intense, sporadic acoustic pulses along networks of grains, or force chains, in the bed of beads.”
Read more from Duke University
“Particle Scale Dynamics in Granular Impact.” Clark, A., Kondic, L., and Behringer, R. 2012. Physical Review Letters, 5:137. DOI: 10.1103/Physics.5.137
Image courtesy of NASA.