Because of the Roadrunner supercomputer’s unique capability,
scientists are for the first time attempting to create atomic-scale models that
describe how voids are created in materials, mostly metals, how they grow, and
merge; how the materials may swell or shrink under stress; and how once broken
bonds might reattach, and they’re doing it at size and time scales that
approach those of actual experiments, so that the models can be validated
experimentally.
Using the reliable SPaSM (Scalable Parallel Short-range
Molecular dynamics) code, adapted to run on Roadrunner, Tim Germann of DOE's Los Alamos National Laboratory is studying the
physics of how materials break up, called “spall,” and how pieces fly off,
called “ejecta,” from thin sheets of copper as shock waves force the material
break apart.
“Our multibillion-atom molecular dynamics code is providing
unprecedented insight into the nature of the critical event controlling the
strength of materials, a fundamental long-standing problem in materials
science,” said Germann.
Some phenomena that can lead to “spall failure” as the
material breaks apart, take place at precisely the time and length scales which
were inaccessible to both simulation and experiment, and so have typically been
described by “trial and error” models that could never be directly verified.
Steady advances in both experimental and simulation
techniques—and supercomputer performance, culminating with Roadrunner—have
closed this gap and are now enabling both simulations and experiments to probe
shock deformation at between 1 and 10 microns, and at nanosecond time scales.
Spall failure and the ejection of material from shocked metal surfaces are
problems that have attracted increased attention both experimentally and
theoretically at Los Alamos. Models are
required that can predict both when a material will fail, and the amount of
mass ejected from a shocked interface with a given surface finish and strength.
Original article
