Dynamic Strength of Silica Glasses at High Pressures and Strain Rates

Citation

Kettenbeil, Christian (2019) Dynamic Strength of Silica Glasses at High Pressures and Strain Rates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RZJW-MX30. https://resolver.caltech.edu/CaltechTHESIS:02202019-104738145

Abstract

Understanding the behavior of silica glasses at high pressures and strain rates is of great importance for geological processes and highly relevant to many technological applications including high-powered laser-matter interactions in optical elements and impact/blast damage in defense systems. Materials typically experience large inelastic deformations at high pressures, which are strongly affected by strength-related phenomena such as work hardening, damage and thermal softening. The pressure-shear plate impact experiment (PSPI) provides detailed information on the pressure and strain rate dependent strength properties of materials subjected to uniaxial compression. However, its range of attainable pressures has so far been limited and the assumptions required for its analysis become invalid at pressures beyond the Hugoniot elastic limit of the anvil materials. In this dissertation, a high-pressure PSPI (HP-PSPI) technique is developed that greatly extends the range of attainable experimental conditions by achieving higher terminal projectile velocities in a powder gun setup. A novel fiber-optic heterodyne transverse velocimeter (HTV) is developed to enable the use of robust frequency-based data reduction techniques, which reduce the effect of signal noise and light coupling losses. A forward analysis method, based on finite element simulations, is employed to match the experimentally observed material response during HP-PSPI experiments on soda-lime glass samples while considering the inelastic deformation of the utilized tungsten carbide anvils. Symmetric HP-PSPI experiments on tungsten carbide revealed a loss of strength at normal stresses exceeding 25 GPa, which hint at active damage or softening mechanisms under nominally uniaxial strain compression. A pressure-dependent strain softening model transitions soda-lime glass from an intact strength of 2.8 GPa, below strains of 10-30%, to a failed granular state following extensive inelastic shear deformation, which accurately predicts the measured response over a wide range of stresses (9-21 GPa) and strain rates (3•10⁵-2•10⁷s^-1). Extending the range of previously attainable pressures and strain rates in PSPI experiments, combined with more robust diagnostics and analysis tools, will greatly benefit our understanding of material strength in extreme environments and enables the investigation of material behavior in a currently unexplored range of pressures and strain rates.

Thesis Files