Identifying the deformation mechanisms of shock-loaded metals

What is it about?

Modern dynamic-compression techniques allow us to compress matter rapidly and reproducibly to temperatures and pressures rivaling those found in planetary interiors. Understanding how exactly metals deform under such extreme loading conditions remains a challenge, in part because the compression takes place so quickly: the short-lived high-pressure states generated by dynamic compression provide a window of only a few nanoseconds' duration in which to collect experimental data. Fortunately, we are now able to thread this temporal needle with the aid of ultrafast x-ray diffraction diagnostics. These allow us to fire subnanosecond-long bursts of high-energy x-rays at a target while it is being dynamically compressed. The angles at which the incoming x-ray beam is scattered encode vital information about the microstructure of the shock-loaded metal. We present a simple model that is in principle able to use the information contained by such x-ray diffraction patterns to deduce which deformation mechanisms (specifically, which 'slip systems') are activated by the dynamic compression process. We test and validate our model using molecular dynamics simulations, which can model metals at the level of their individual atoms. We further show that our model outperforms similar kinematic models that have recently been used to interpret high-profile dynamic compression experiments.

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Photo by Aryo Yarahmadi on Unsplash

Photo by Aryo Yarahmadi on Unsplash

Why is it important?

Quantitatively measuring the deformation mechanisms of metals under rapid dynamic compression remains a challenge in experimental shock physics. Knowing which mechanisms are activated will ultimately inform the rapidly-evolving field of 'extreme materials science', whose purpose is to explain the basic behavior of condensed matter at extraordinary densities, temperatures, and strain rates. Such knowledge could help us to understand, for instance, the kind of hypervelocity impact events that occur between meteorites and planets, or being space debris and satellites.