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Plastic deformation of metals results from the motion of a high density of dislocation lines. A strong shock produces an unusual number of dislocations within a metal’s crystalline lattice, which changes the metal’s mechanical properties such as strength, ductility and resistance to fracture and cracking.

In a paper published in the Sept. 17 edition of the journal Nature Materials, Livermore researchers, in conjunction with scientists from the University of Oxford, have compared and validated strong shock molecular dynamics simulations to dynamic experimental data in metals.

“We calculated the time needed for the metal to generate defects and relax in a strong shock wave,” said Eduardo Bringa, LLNL’s lead author of the paper. “We came to understand this time interval in terms of the time needed for line defects (dislocations) to move far enough to relax the strain. It was known that the more dislocations that are produced and the more they move, the more the strain is relaxed.”

However, the researchers had a surprise: If the dislocations form too rapidly, they become entangled before they can move far enough to relax the strain. In a ramped pressure wave (rather than an abrupt shock), fewer dislocations form, but they are more effective at relieving the strain because they are freer to move.

“Comprehending this kinetic time scale has unified our understanding of how the tremendous transient stresses in shock waves are compatible with our tried and true understanding of material strength in everyday conditions,” said Robert Rudd, an LLNL co-author of the paper.

“This provides a powerful tool to explore new regimes in the emerging field of materials science at extreme conditions, such as those expected in experiments planned for NIF,” said Bruce Remington, who leads a group developing such experiments for the National Ignition Facility.

A team including several LLNL researchers previously used time-resolved X-ray diffraction to measure the microscopic lattice response and relaxation behind the shock front in a single crystal piece of copper. The shocked copper relaxed in less than one nanosecond and the current simulations reproduce this timescale. Such large-scale simulations were possible, for the first time, due to the extensive computational power of LLNL supercomputers.

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4 Comments

  1. cool template!!!
    *envy*

  2. i didnt do it & what do you really mean y saying “envy”?
    get outta my blog, smto!

  3. I wanna stay here for the rest of my life!
    SMTO BACK

  4. KICK ASSSSSS


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