Bounds on the Rate-Dependent Plastic Flow of Tantalum up to 75 GPa

• Published in: Journal of dynamic behavior of materials 2021-06, Vol.7 (2), p.307-324
• Main Authors: Reed, B. W., Patterson, J. R., Nguyen, J. H., Stölken, J. S., Kumar, M.
• Format: Article
• Language: English
• Subjects: Ballistics; Chemistry and Materials Science; Free surfaces; Gas guns; High strain rate; Interpolation; Materials Science; Metallic Materials; Plastic flow; Pressure dependence; Rarefaction; S.I. : High Pressure Strength; Shock loading; Shock wave propagation; Shock waves; Solid Mechanics; Spline functions; Stresses; Systematic errors; Tantalum
• ISSN: 2199-7446; 2199-7454
• DOI: 10.1007/s40870-021-00296-6

We report on the continued development of thermodynamics-based analysis of shock waves propagation with the objective of extracting information related to materials strength at high strain rates and pressures. Building on previous results reported for peak stresses of 10 GPa and 25 GPa, we present a series of three-step gas-gun shock experiments designed to explore the pressure and strain rate dependence of plastic flow in polycrystalline tantalum. These experiments at nominal peak stresses of 50 GPa and 75 GPa show the irreversible deformation before pullback to be almost entirely confined to the shock loading, with negligible plastic relaxation on the post-shock plateau. We also add a reverse-ballistics shot at 25 GPa, which was designed to reveal the pullback response with negligible interference from free-surface effects. General thermodynamic considerations allow us to place bounds on the plastic behavior even for parts of the curve that change far too rapidly for the velocimetric time resolution of (conservatively) ~ 5 ns. To analyze the data, we found it necessary to substantially improve the interpolation/extrapolation scheme in order to improve its robustness, flexibility and range of applicability. We describe the new scheme based on splines, as well as an extension of free-surface corrections to the post-shock rarefaction waves. Reanalysis with the new scheme produces results essentially within the error bars previously reported, showing that the known systematic errors associated with free-surface effects are relatively inconsequential for determining thermodynamic paths.