Potentially overlooked high post-shock temperatures in dynamic compression experiments

Shock experiments provide an understanding of how materials react under extreme conditions, with applications for astrophysics, geophysics, material science, and more. These are thermodynamically irreversible processes, requiring measurements at micrometer-level spatial resolutions and nanosecond temporal resolutions.

Calculating the temperature across the shock front as well as residual temperatures is especially challenging. A few experimental methods have been developed to measure the temperatures under dynamic shock compressions, but the short timescales at which these experiments take place make it difficult to separate the effects of compression and heating.

Using ultra-fast X-ray probes, Yang et al. found unexpectedly high temperatures after shock using thermal expansion measurements. To validate their observations, the team investigated the thermal response of aluminum (Al) and zirconium (Zr) by numerical simulations.

“We found higher than expected post-shock temperatures of Al and Zr, which indicates that the defect-mediated shock heating largely cancels out thermal elastic cooling effects,” said author Hong Yang. “The common understanding of shock release as an isentropic process is challenged by our observations.”

The heating effects the team found are likely a common but overlooked effect in laser shock experiments. One application of this phenomenon is the examination of paleomagnetic records involving frequent shock events; another is the interpretation of free surface velocity results from velocity interferometer experiments.

“Because temperature changes almost every material property, this heating effect can potentially change the explanation of many experimental results,” said Yang. “Others can employ similar experimental designs to try to capture the heating process in their samples for shock experiments. It would also be interesting to model the energy conversions in this process.”

Source: “Evidence of non-isentropic release from high residual temperatures in shocked metals measured with ultrafast x-ray diffraction,” by Hong Yang, Michael R. Armstrong, Ryan A. Austin, Harry B. Radousky, Akshat Hetal Patel, Tiwei Wei, Alexander F. Goncharov, Wendy L. Mao, Eduardo Granados, Hae Ja Lee, Inhyuk Nam, Bob Nagler, Peter Walter, Jonathan L. Belof, Shaughnessy B. Brown, Vitali Prakapenka, Sergey S. Lobanov, Clemens Prescher, Nicolas Holtgrewe, Elissaios Stavrou, Paulius V. Grivickas, and Arianna E. Gleason, Journal of Applied Physics (2024). The article can be accessed at https://doi.org/10.1063/5.0217779 .