Constraining flow stress models at high strain-rates through in-situ imaging of hole closure under dynamic compression*

The stress at which a material plastically flows depends on the current state of the material, strain-rate, and microstructure among other quantities. Experimental tests at high strain-rates (\textgreater 10$^{\mathrm{3}}$/s) often use measurement of shape change to infer flow stress behavior and are facilitated by comparisons with advanced simulations. A new plate-impact experimental test will be described consisting of in-situ x-ray imaging the closure of a cylindrical hole in a sample during the passage of a pressure pulse of controlled amplitude and duration. Experiments on tantalum aims to test the validity of present flow stress models within the experimental uncertainty. Results will be compared with direct numerical simulations using several flow stress models. We will discuss the results, the sensitivity of this new experimental test, and the implications for informing models.