Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Metal deformation studies lead to new understanding of materials at extreme conditions

20.09.2006
Researchers have found a new tool to explore materials at extreme conditions.

By combining very large-scale molecular dynamics simulations with time-resolved data from laser experiments of shock wave propagation through specific metals, scientists at the Lawrence Livermore National Laboratory are now able to better understand the evolution of high-strain-rate plasticity.

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.

Shock compression of condensed matter occurs in a variety of situations including high-speed automobile and aircraft collisions, explosive welding, armor penetration, meteor impacts, interstellar dust dynamics, and inertial confinement fusion. A detailed understanding of the three-dimensional lattice relaxation process during shock compression beyond the elastic limit had not been achieved previously.

"These results will help us understand what to expect during the extreme material deformation experiments, and better design those experiments," Rudd said. "High rate material deformation is important in explosive fragmentation, penetration, collision, and so on, from the prosaic automobile crash, to the kind of penetration scenarios of interest to homeland security.

The Laboratory's defense-related mission requires an understanding of how metals respond to sudden shock waves and subsequent high-strain-rate deformations. To assess materials properties and performance under extreme deformation conditions, researchers work to understand the fundamental origin of deformation and strength and how the resistance against plastic deformation arises from the collective dynamics of lattice dislocations.

"In our planned materials experiments, we intend to deform a solid-state metal at extraordinary pressures and strain rates," said Remington. "Eduardo has shown us a very promising way for interpreting the results.

Concludes Bringa: "The experiments and simulation combination makes a powerful pair for exploring uncharted even unimagined regimes of material dynamics."

Anne Stark | EurekAlert!
Further information:
http://www.llnl.gov/pao/news/releases.html

More articles from Materials Sciences:

nachricht Let the good tubes roll
19.01.2018 | DOE/Pacific Northwest National Laboratory

nachricht Method uses DNA, nanoparticles and lithography to make optically active structures
19.01.2018 | Northwestern University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>