Granular Flow of an Advanced Ceramic under Ultra-High Strain Rates and High Pressures

The dynamic rheology of a complex granular material system strongly depends on the imposed stress state. However, drawing a clear physics based picture of dynamic granular flow is challenging due to the heterogeneous nature of granular materials, as well as the overwhelming difficulties in carrying out dynamic experiments. Here, pressure-shear plate impact (PSPI) is utilized to load a granular boron carbide ceramic in a multi-axial fashion with strain rates on the order of 10(5) s(-1) and pressure levels ranging from 1 to 3 GPa. Comparisons between the shear flow stresses and the superimposed normal stress indicate a strong pressure dependence in the constitutive response, along with an effective friction coefficient measured to be around 0.16. Both the normal and shear stress-strain relations are obtained. Granular boron carbide shows a highly compressible behavior with a significant amount of volume compaction achieved as the result of the large uniaxial normal strain. Due to the compaction, the estimated granular wave speed increases with density. Microstructure characterization of the deformed particles shows that fracture and amorphization are active deformation mechanisms besides the grain-grain frictional interactions and particle rearrangement. This study will contribute to the development of integrative modeling for behavior of granular boron carbide at ultra-high strain rates and confinement pressures. (C) 2020 Elsevier Ltd. All rights reserved.