BUFFALO, N.Y. -- A University at Buffalo theoretical physicist
who published research in 2001 demonstrating that it someday may be
possible to build bridges, buildings and other structures that are
nearly blast-proof, now has published results based on computer
simulations showing how a shock-absorption system might be
constructed to accomplish that goal.
Published in October in Physical Review Letters, the research is
relevant not only to questions of shock-absorption in these
structures, but also to life-saving improvements in tanks and
aircraft carriers, as well as bullet-proof vests and other
protective clothing for soldiers, law enforcement officers and even
The simulations are of critical importance because they allow
researchers and manufacturers to see how a potential system might
work without having to painstakingly construct the systems and
spend $40,000 to conduct a single blast in a test facility.
In earlier UB research by the same scientists, granular systems
composed of individual spheres of gradually reduced size -- a
"tapered" chain in a casing -- proved to be capable of efficiently
absorbing well over 80 percent of input energy.
The main findings of the current research are that it is
possible to retain the scalability of the system, reduce its size
by a factor of five and make it far more capable of absorbing
The key to achieving the results, according to Surajit Sen,
Ph.D., UB professor of physics and co-author of both the current
work and the 2001 publication, was the use of interstitial grains
of the right sizes to control energy propagation through the
"It turns out that the shock pulse is more easily managed when
tiny interstitial grains are placed between the many progressively
shrinking spheres or grains that make up the tapered chain," he
In the most recent paper, the UB physicists reported that this
"decorated, tapered chain" system is capable of absorbing more than
50 percent of the shock that could not be absorbed by previous
systems they had simulated.
These greater shock absorption capabilities were attributed to
the use of tiny, interstitial grains or
particles of only about a millimeter that were placed in between
each sphere, the "decorated" part of the chain; it turned out that
the smaller these grains were, the more shock absorption they could
"These tiny grains were able to accomplish a huge trick," said
Sen, co-author of the paper with Robert Doney, doctoral candidate
in the Department of Physics in the UB College of Arts and
Sciences. "They trap energy as it flows from the larger to the
smaller grain, slowing it down. As it slows down, the smaller grain
then essentially rattles back and forth between its two bigger
neighbors, dissipating much of the energy as heat and sound."
Because the granular shock-absorbing system is strongly
nonlinear, he said, the system allows directed energy transfer and
the smaller grains undergo rapid rattling, which helps to
efficiently distribute and dissipate the energy.
The simulations are significant because they have modeled shock
pulses traveling at speeds approaching those encountered in combat
situations, Sen said.
"These were simulations of pretty large impact shock pulses,
traveling at several hundred meters per second," he explained, "and
when we have such large impacts, the grains themselves now behave
like sponges, absorbing the energy."
The simulations showed that in some of the larger impacts, the
system would remain effective, but that significant and
irreversible deformation would occur.
Sen explained that the system is proving to be very scalable, so
that it could be designed to handle almost any typical shock.
According to the UB scientists, their earlier predictions about
the shock-absorbing capabilities of these "tapered chain shock
absorbers" were experimentally confirmed in publications in
Granular Matter (2004) by independent researchers at the Colorado
School of Mines in collaboration with a group at the NASA Glenn
Research Center, as well as in Physical Review E (2006) by
researchers at the University of Santiago in Chile and the Superior
Institute of Mechanics (SUPMECA) in Paris.
The UB research is funded by the U.S. Army Research Office.
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