Iron Response in Extreme Compression and Tension Regimes: Complementary NIF and Janus Experiments

Iron is the major component of the Earth’s solid inner core, so determining its strength under extreme conditions is crucial to understanding the rheology of Earth’s core and interpreting geophysical observations. Although it has been widely accepted that body centered cubic Fe will go through at least one, possibly more, phase transitions at high pressures, the influence of such a reversible phase transition on the strength of Fe is still unknown. Molecular dynamics simulations of shock-compressed single crystal bcc iron show that the newly formed epsilon phase is nanocrystalline. Strength dependence on grain size and strain rate has been investigated through campaigns at NIF and JLF. Preliminary results show that at ultra-high strain rates, initial grain size has no effect on material strength while at lower strain rate, minor effects can still be seen. The strength of iron at Earth core conditions achievable with NIF was found to be approximately 16 GPa, which is remarkably high. These results will lead to an improved understanding of asteroid impact dynamics, planetary formation dynamics, and interior structures of the earth, planets and exoplanets.