Monday  |  Lakeshore A  |  02:40 PM–03:00 PM

#19551, In-material Particle Velocity Measurements of Dynamic Sheared Materials

Particle velocity measurements in shock compression experiments provide a full continuum description of various phenomena including elastic-plastic transition, equations of state (EOS), and even phase transformations. In conventional experiments, the free surface velocity is measured using laser interferometry (e.g., photon Doppler velocity (PDV)) from which the particle velocity is inferred. However, at the free surface, the material releases to zero stress which can be disadvantageous for certain experiments where a constant stress state at the target is necessary. For this reason, in-material measurements using optical windows in shock compression experiments are essential. They open avenues to explore interesting phenomena such as probing pressure-dependent material properties, and phase transition kinetics. Despite the importance, in-material velocity measurements using laser interferometry in pressure-shear plate impact (PSPI) experiments have been limited. Additionally, there have been no instances of window interferometry used in PSPI experiments using PDV in the infrared spectrum and at high pressures where the interesting phenomena mentioned above are more prominent. In this study, the capabilities of window interferometry for PSPI experiments are extended to high pressures using two window materials: (a) lithium fluoride (LiF) [100] and (b) c-cut sapphire. First, an overview of the diffraction grating design is discussed, followed by a symmetric window PSPI experiment on Aluminum using LiF windows to validate the experimental technique. As an extension, experiments are conducted on bcc iron, using a sapphire window, at pressures ranging from 10-15 GPa to extract the evolution of the elastic wave speeds during phase transformation. Finally, this data is used to explore the role of shear on the transformation kinetics.

Vatsa Gandhi   University of California, Los Angeles
Michael Mello   California Institute of Technology
Barry Lawlor   California Institute of Technology