Materials At Extremes: Shock-induced Fracture and Phase Transitions

Abstract

Owing to the high-pressures and strain-rates associated with shock waves, their study is of great interest to a host of different fields including, but not limited to, planetary sciences, medical applications, sports science, aerospace engineering, chemistry, and materials science. Most broadly, the study of shock wave can be broken into two categories; the destructive and the constructive. On the destructive side, researchers are investigating the deleterious effects of shock waves in primary traumatic brain injury, earthquakes, and material fracture. On the constructive side, advances in shock wave generation have allowed researchers to leverage the high-pressures and high-strain rates associated with shock waves in medical practices, such as shock lithotripsy used to break up kidney stones, in the high throughput testing of novel materials, and in the generation of exotic states of matter.

Expanding on previous experimental developments, the work presented herein employs laser-induced converging shock waves for the efficient generation of shock waves at the microscale. This technique allows one to conduct hundreds of experiments in a day on small sample volumes, all with a conventional tabletop pulsed laser system. Converging ring shocks were used to drive the insulator-to-metal phase transition in the prototypical Mott-Hubbard system, vanadium sesquioxide V2O3. The phase transition and mechanism were interrogated with Raman spectroscopy and optical photothermal IR microscopy of recovered samples, as well as in situ time-resolved optical reflectivity measurements during shock propagation. Herein we present, to the best of our knowledge, the first permanent pressure-induced insulator-to-metal phase transition in V2O3.

The fracture response of brittle and ductile materials were studied with converging laser-induced surface acoustic waves (SAWs) and high-speed imaging. Borosilicate glass samples subject to converging SAWs demonstrated anomalous fracture-toughness enhancement above a shock pressure threshold. Raman spectra of recovered samples revealed significant structural rearrangements in the glass amorphous structure. We hypothesize that these rearrangements allow for nanoscale ductility that provides a mechanism for energy relaxation in shocked silica glasses above a given shock pressure threshold. Additionally, preliminary results regarding SAW-induced melting in metal samples are presented.