X-ray diffraction images show how shock affects the crystal structure of copper at the atomic scale
An international team, including Oxford University scientists, has used the powerful X-ray laser at the US Department of Energy's SLAC National Accelerator Laboratory to create atomic-scale movies of 'the ultimate spring'. Normally, when a metal is crushed suddenly, as during an impact, it deforms and buckles, with the atoms re-arranging themselves in a complex way to take up the deformed shape - and usually only small pressures allow a metal to 'bounce back' like a spring. However, by subjecting a piece of copper to a pressure equivalent to nearly a quarter of that of the centre of the earth within just a few tens of trillionths of second, the team found the atoms had no time to re-arrange and instead acted just like a perfect spring right up to the theoretical breaking point of crystalline matter - where the atoms would spontaneously slide over each other. The team's results pinpoint the precise breaking point when the extreme pressures began to permanently deform the copper structure, or lattice, so it could no longer retain its perfect spring-like response. It also confirmed the accuracy of complex computer simulations that model the behavior of hundreds of millions of atoms within micron-sized samples of material. Such simulations are used to design stronger, more durable materials - such as shielding for satellites to withstand high-speed pelting by space debris - but they have been hard to test in the lab because of the tiny samples and short timescales involved. Movies like these will help researchers create new kinds of materials and test the strength of existing ones. Watch a movie showing how shock impacts on copper here.
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