Final Report for Aoard Grant Fa2386-11-1-4101 " Effect of Grain Scale Properties on Bulk Deformation of Granular Deposit Due to High Speed Projectile Impact "

In order to understand the mechanical behavior of granular deposit subjected to high-speed projectile impact, we perform both physical experiments and grain-scale numerical simulations. In the high-speed impact experiment, we adopted a new technology to observe the deceleration of projectile after penetrating into sand layer. The observed results together with simple one-dimensional model with Rankine-Hugoniot equations suggests the importance of grain-scale mechanics such as grain crushing to evaluate the evolution of material parameters. Grain-scale observation of the specimen after the experiment by micro x-ray CT revealed that the grain crushing is a key phenomenon for evaluating projectile motion. Then a series of numerical simulation using Discrete Element Method were performed and the compression behavior of granular materials was analyzed in terms of grain crushing. The results suggest the transition of three material phases; (1) elastic regime as a granular matter, (2) plastic regime due to grain crushing, and (3) Hugoniot solid regime, and they are the important ingredients for modeling the equation of state of granular materials subjected to high speed compression. Based on the above-mentioned observations, we constructed the EOS which covers wide range of deformation rate; from quasi-static deformation to high-speed impact, because the projectile deceleration process is affected not only by the initial high-speed regime but also the subsequent slow deformation regime. The proposed EOS was validated both with the existing impact experiment and with the quasi-static 1D compression test. Moreover, we also found that the material parameters for granular materials can be obtained from those for the host rock. Finally, we demonstrated the applicability of the proposed EOS into high-speed projectile impact experiment. It turned out that the projectile deceleration behavior observed in the experiment is a consequence of the complicated compression behavior of sand deposit.