#atomic vibrations

[materialsscienceandengineering]

Atomistic simulations go the distance on metal strength

Lawrence Livermore National Laboratory researchers have dived down to the atomic scale to resolve every "jiggle and wiggle" of atomic motion that underlies metal strength.

In a first of its kind series of computer simulations focused on metal tantalum, the team predicted that, on reaching certain critical conditions of straining, metal plasticity (the ability to change shape under load) meets its limits. One limit is reached when crystal defects known as dislocations are no longer able to relieve mechanical loads, and another mechanism - twinning, or the sudden reorientation of the crystal lattice - is activated and takes over as the dominant mode of dynamic response.

The research appears in the Sept. 27 edition of Nature as an Advance Online Publication.

Strength and plasticity properties of a metal are defined by dislocations, line defects in the crystal lattice whose motion causes material slippage along crystal planes. The theory of crystal dislocation was first advanced in the 1930s, and much research since then has focused on dislocation interactions and their role in metal hardening, in which continued deformation increases the metal's strength (much like a blacksmith pounding on steel with a hammer). The same simulations strongly suggest that the metal cannot be strengthened forever.

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[materialsscienceandengineering]

New modeling method focuses attention on amorphous material's unusual vibrational modes

Asegun Henry wants to avert the worst effects of climate change by finding new forms of renewable energy and improving the materials that contribute to energy use.

"The way we produce electricity today pollutes the environment," said Henry, a mechanical engineering professor at Georgia Tech. "My research is primarily centered on converting us from a fossil fuel-based infrastructure to a renewable- or solar-based infrastructure so we can rely on renewable forms of energy that don't pollute the world at all.

"I personally see that as saving the world."

What makes Henry's approach to energy problems different from other engineers is his background in atomic-level computer modeling.

"I understand different processes in terms of what's going on at the atomic level," Henry said. "That allows me to develop insights and opportunities for new ideas that are different from others that are coming from the macroscopic level."

His research is largely interested in how heat transport works at the smallest scales.

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