Giving the slip to a metal deformation mystery

Dynamic compression can squeeze matter to pressures akin to planet interiors in less than a few nanoseconds, but researchers struggle to understand exactly how metals deform under this type of force. While it is known that their deformation involves shearing on slip planes, it is challenging to identify which slip systems, or which combinations of slip planes and shear directions, are involved.

Patrick Heighway and Justin Wark developed and tested a kinematic model that could identify active slip systems in a dynamically compressed metal from its X-ray diffraction pattern.

Because dynamic compression usually destroys metals, all measurements must be taken during their nanosecond-long deformation. X-ray diffraction is fast enough to capture how a metal’s crystal structure changes during this process.

The authors’ early-stage model is able to determine what slip systems are active, and by how much, from these crystal structure changes. This knowledge could help the rapidly evolving field of extreme condition materials science.

“Knowing which slip systems are activated during dynamic-loading scenarios will ultimately inform our understanding of fundamental materials behavior under extreme loading conditions,” Heighway said. “Such conditions might be encountered, for example, during planetary or meteoric impact events, or during a hypervelocity impact between a satellite and a rogue piece of space debris.”

The authors also compared their model to two preexisting kinematic models using molecular dynamics simulations. They found that, unlike their model, the preexisting models fail to predict crystal rotation of metals under uniaxial strain.

Real dynamic compression of metals is more complex than the authors’ simulations, so they will continue to test and refine their model before eventually applying it to an actual experiment.

Source: “Kinematics of slip-induced rotation for uniaxial shock or ramp compression,” by P. G. Heighway and J. S. Wark, Journal of Applied Physics (2021). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0038557 .