The paper, by Levitas and Ramon Ravelo, a collaborator from Los Alamos National Laboratory, “Virtual melting as a new mechanism of stress relaxation under high strain rate loading,” describes a new theory of short-term melting of materials followed by immediate recrystallization. The paper was originally published in the Proceedings of the National Academy of Sciences of the United States of America (Levitas and Ravelo, PNAS, 2012, Vol. 109, 13204).
Levitas and Ravelo discovered a new mechanism of plastic deformation in shock waves. Using a new thermodynamic approach under nonhydrostatic loading, or loading that is different in different directions, as well as simulations at the atomic level, the researchers proved that in very strong shock waves, material can melt at up to 4,000K below the melting temperature.
Their findings will be relevant for studying nuclear explosions and meteorite impacts, as well as for planned experiments in large laser facilities such as the National Ignition Facilities at the Lawrence Livermore National Laboratory in the U.S. and LULI (the Laboratoire pour l’Utilisation des Lasers Intenses) in France.
The feature also connects the PNAS paper with previous Levitas papers on virtual melting as mechanisms of a crystal-to-crystal phase transition, high-pressure amorphization, and surface-induced transformation in a crystalline nanofiber, all much below the melting temperature.
In addition, the paper was featured in an interview “Crystals take a chill pill: A thermomechanical theory of low-temperature melting,” published at Phys.org.
In the interview, Levitas discussed next steps in their research.
“We plan to extend our thermodynamic approach for arbitrary 3D loading – in particular for deformation under high pressure and shear strains. It can also be extended for amorphization and sublimation, which can be considered as mechanisms of stress relaxation. Applying a phase field approach to the phenomena discussed is another important task,” Levitas said. “Finally, in molecular dynamic simulations we’ll study polycrystalline metals and materials with suppressed plasticity.”
Read more at Nature Materials: http://www.nature.com/nmat/journal/v11/n9/full/nmat3411.html
Read more at Phys.org: http://phys.org/news/2012-08-crystals-chill-pill-thermomechanical-theory.html#jCp