10.31.13

Stress Actually Makes You Stronger … At Least Some of the Time

Researchers at SLAC test the mettle of metals, with potential benefits for all.

Click to enlarge photo.Enlarge Photo

These thin samples of copper, iron and titanium were shocked with optical laser pulses and probed with SLAC's X-ray laser, the Linac Coherent Light Source (LCLS).Photo courtesy of SLAC National Accelerator Laboratory

These thin samples of copper, iron and titanium were shocked with optical laser pulses and probed with SLAC's X-ray laser, the Linac Coherent Light Source (LCLS).

"Stress makes you stronger." So people say … especially those who don't seem especially stressed. But there might be an 'element' of truth to the matter, as shown by a team of researchers at the Office of Science's SLAC National Accelerator Laboratory (SLAC), and their recent paper in Science magazine.

That team, led by Despina Milathianaki and including collaborators from Lawrence Livermore National Laboratory, Stanford University and the University of Oxford), put extreme stress on the element copper. Instead of pointing out that the holidays are scarcely a month away and the copper hadn't even started to think about its shopping – though that would probably have worked – the scientists led by Despina Milathianaki instead simply stressed, and shocked, the copper by using SLAC's powerful X-ray laser. (Actually, since the process of science – and getting published in Science, takes time, the research was done well before the paper appeared.)

The X-ray laser, more formally known as the Linac Coherent Light Source, or LCLS, produces tightly focused X-ray bursts that are billions of times brighter than conventional hospital X-ray machines. It produces bursts that last for 50 femtoseconds, or 50/1,000,000,000,000,000 seconds. An eye-blink is an age at such timescales, and the LCLS is so fast that it can capture atoms in action, and even make movies of molecules in motion (popcorn optional, precision mandatory).

That's exactly what the researchers did. They blasted a thin layer of copper with pulses from an optical laser, while simultaneously probing the copper structure with pulses from the LCLS. The copper layer was so thin, about one-thousandth of a millimeter (one micron), and the pulses were so strong and fast, that SLAC scientists could actually see the copper stress, and then break, deformed irreparably from its original shape.

Using the LCLS, researchers could see the instant that the copper broke, as well as the micro-moments immediately before and afterwards; strobe-like images that they assembled into an atomic-scale movie http://www.youtube.com/watch?v=wx5bzv9j_mQExternal link. SLAC scientists then put similar stress on several other metals, including iron and titanium.

Click to enlarge photo.Enlarge Photo

A diagram of the setup used in the ultrafast shock compression experiment at SLAC's Linac Coherent Light Source (LCLS), including a large-area CSPAD detector, X-ray and optical lasers, and thin copper samples.Photo courtesy of SLAC National Accelerator Laboratory

A diagram of the setup used in the ultrafast shock compression experiment at SLAC's Linac Coherent Light Source (LCLS), including a large-area CSPAD detector, X-ray and optical lasers, and thin copper samples.

Admittedly, this begs the question of why anyone would want to test the mettle of a metal, much less make movies of its shock. It turns out that there are good reasons for doing so.

First, the stress also serves as a direct test of supercomputer simulations that model how metals behave. The better the data that goes in, the more reliable are the results that come out. That's important in trying to model the exact behavior of metals under stress, say the crash of a car or the impact of a bullet into armor. And it's especially important for the Office of Science, since several of its labs are home to world-class supercomputers, which researchers are using for everything from simulating the 'subatomic soup' of the early universe to modeling air turbulence and thereby improving airplane performance.

Those better metal models could, in turn, lead to the design of even stronger and more durable materials. And those materials might come in handy for technologies that operate in extreme environments, such as shielding for satellites and space probes. They'll likely be useful in more everyday applications too.

So it turns out that some clichés have an element of truth – stress can make you stronger. Just don't tell that to someone who's already stressed.

This research was supported by the Linac Coherent Light Source's (LCLS) in-house research program. SLAC's LCLS is the world's most powerful X-ray free-electron laser. A DOE Office of Science national user facility, its highly focused beam shines a billion times brighter than previous X-ray sources to shed light on fundamental processes of chemistry, materials and energy science, technology and life itself. For more information, visit lcls.slac.stanford.eduExternal link.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about SLAC, please go to: http://www.slac.stanford.edu/External link.

Charles Rousseaux is a Senior Writer in the Office of Science, Charles.rousseaux@doe.science.gov.

Last modified: 10/31/2013 9:42:38 AM