Apache Leap tuff rock: High strain rate characterization and support simulations

Abstract
Yucca mountain is being closely studied as a possible repository for high-level radioactive waste. The rock found at the Yucca Mountain site, i.e. Nevada tuff, is, consequently, of immediate interest. Since it is difficult to obtain samples of the actual Nevada tuff the Apache Leap tuff rock, from Arizona, has been chosen as a similar alternative for this study. The Apache rock was tested in compression at low (10 ^{- 4} s ^{- 1}) and high (10² -10³ s ^{- 1}) strain rates to evaluate its strain rate dependence. Some of the dynamic tests were performed with a pulse shaper. Strain in the sample was measured with strain gages. Numerical simulations of the full Hopkinson Bar with and without pulse shaper were performed with LS-DYNA. These were very useful in understanding interpretation of the experimental results. Both incident and output waves measured in the SHPB compared very well with the waves obtained from LS-DYNA simulations, confirming that the constitutive model used for the rock was a realistic one. The main conclusions from this work are: 1) The SHPB is a reliable method to obtain the constitutive model of the rock at high strain rates. 2) The pulse shaper use is advised but not compulsory to obtain reliable data, 3) the Apache tuff rock is not strongly sensitive to strain rate.