Transverse Photonic Doppler Velocimetry for Plate Impact Experiments

Citation

Bischann, Moriah Nicole (2017) Transverse Photonic Doppler Velocimetry for Plate Impact Experiments. Senior thesis (Major), California Institute of Technology. doi:10.7907/Z9GB224C. https://resolver.caltech.edu/CaltechTHESIS:06012017-131024630

Abstract

High-pressure shock waves propagate in materials when automobiles collide, projectiles impact against bunkers, and mining charges detonate beneath Earth's surface. It is difficult to quantify the behavior of materials experiencing such sudden and high pressures. Specialized interferometry techniques have enabled the study of rapid, high-strain-rate deformation during controlled plate impact testing.

Transverse motion during plate impact experiments is currently measured with the transverse displacement interferometer (TDI). However, the TDI does not take advantage of modern telecommunications technology and data analysis techniques that allow for the measurement of high velocities (in the km/s range) with fine time resolution. We designed and developed a transverse photonic Doppler velocimetry (TPDV) technique for plate impact experiments based entirely on fiber optic components. The TPDV system uses light diffracted from a grating to capture transverse motion. This signal is frequency upshifted to achieve more fringes per unit time. Data is analyzed using spectral analysis techniques to detect micrometer displacements on a nanosecond to microsecond timescale.

We demonstrated the TPDV technique's capabilities with normal impact of single crystalline y-cut alpha-quartz against borosilicate. We simultaneously collected photonic Doppler velocimetry (PDV) measurements of longitudinal displacements. Finally, we compared our longitudinal and transverse experimental results to theoretical calculations. Our data's orthogonal velocity jumps showed that the TPDV technique accurately detected transient velocities and the magnitudes of longitudinal and shear waves.

Our TPDV technique will facilitate the study of deformation and failure of materials during normal and pressure-shear plate impact. Comprehending shock-wave dominated deformation in materials is important for the design of aerospace structures, understanding planetary impact, and creating shock-mitigating materials.

Thesis Files