Validation of the copper equation of state via shock loading experiments of loosely associated powders

TL;DR

This study validates a modified copper equation of state through shock experiments on porous powders, showing good agreement with models and highlighting the importance of lattice heat reduction at high temperatures.

Contribution

It provides experimental validation for a revised two-phase copper EOS using shock loading of powders with controlled porosity.

Findings

Good agreement between measured Hugoniot and the new EOS model

Significant softening observed above ~156 GPa in copper

Unloading behavior matches hydrodynamic simulations with the new EOS

Abstract

High-fidelity shock experiments were performed on copper powders with controlled porosity via improved target fabrication and assembly. Optical velocimetry and multi-channel pyrometry were used to obtain Hugoniot data, isentropic release paths, and interface temperature histories. The results validate a modified two-phase equation of state (EOS) for copper based on the framework of Greeff et al. The measured Hugoniot shows good agreement with the present model but exhibits significant softening above ~156 GPa relative to the original Greeff EOS, indicating that reduction in lattice specific heat becomes essential when shock temperatures exceed three times the melting point (T > 3Tm). Unloading behavior matches hydrodynamic simulations incorporating the recalibrated EOS, confirming its accuracy for off-Hugoniot states. Theoretical analysis of temperature release profiles suggests that the thermal conductivity of shocked copper powders may be considerably higher than first-principles predictions. Crucially, despite heterogeneity in shock heating, the macroscopic dynamic response of copper powders with a porosity of ~1.7 is well captured by an average-density EOS model, supporting the use of porous material experiments for EOS validation under extreme conditions.