Structure of shock waves in particulate composites

Abstract

The shock compression response of particulate heterogeneous solids was investigated using normal plate impact experiments and numerical simulations. A model composite system of silica glass spheres embedded in a matrix of thermoplastic polymer, polymethyl methacrylate, was developed to mimic the impedance mismatch of structural and energetic heterogeneous materials. Shock wave profiles were measured at multiple points on the rear surface of the composite specimens to characterize shock dispersion and spatial heterogeneity in material response due to the random distribution of particles. Composites with single mode as well as bimodal bead diameter distributions were subjected to plate impact loading at ∼1000 m/s resulting in an average shock stress of ∼4 GPa. Shock rise times were measured for composites of 30% and 40% glass by volume, with spherical particles of diameters in the range of 100–1000 μm. In the case of single mode composites, the shock wave rise times were observed to scale linearly with particle diameter divided by the bulk shock wave speed. The addition of a second bead size to a base size in a 30% glass by volume composite mix resulted in significant increases in shock rise time. Numerical simulations were used to develop insights into scattering and the development of shock structure in particulate composites. Shock disruption mechanisms due to particles and matrix/interface damage effects are discussed.